ISSN Online: 2152-7393 ISSN Print: 2152-7385

DOI: 10.4236/am.2019.1010057 Sep. 27, 2019 805 Applied Mathematics

**On the First and Second Locating Zagreb **

**Indices of Graphs **

**Suha A. Wazzan**

**1***

**, Anwar Saleh**

**2**

1_{Department of Mathematics, Faculty of Science, KAU King Abdulaziz University, Girls Campus, Jeddah, KSA }
2_{Department of Mathematics, Faculty of Science, University of Jeddah, Jeddah, KSA }

**Abstract **

By the distance or degree of vertices of the molecular graph, we can define graph invariant called topological indices. Which are used in chemical graph to describe the structures and predicting some physicochemical properties of chemical compound? In this paper, by introducing two new topological in-dices under the name first and second Zagreb locating inin-dices of a graph G, we establish the exact values of those indices for some standard families of graphs included the firefly graph.

**Keywords **

Zagreb Indices, First and Second Locating Indices, Join Graph, Firefly Graph

**1. Introduction **

Topological indices play a significant role mainly in chemistry, pharmacology,
etc. (see [1]-[7]). Many of the topological indices of current interest in
mathe-matical chemistry are defined in terms of vertex degrees of the molecular graph.
Two of the most famous topological indices of graphs are the first and second
Zagreb indices which have been introduced by Gutman and Trinajstic in [8],
and defined as *M G*1

### ( )

=### ∑

*u V G*∈

_{( )}

### (

*d u*

### ( )

### )

2 and*M G*2

### ( )

=### ∑

*uv E G*∈ ( )

*d u d v*

### ( ) ( )

, respectively. The Zagreb indices have been studied extensively due to their nu-merous applications in the place of existing chemical methods which need more time and increase the costs. Many new reformulated and extended versions of the Zagreb indices have been introduced for several similar reasons (cf. [9]-[17]).One of the present authors Saleh [18] has recently introduced a new matrix
representation for a graph G by defining the locating matrix **Lo**

### ( )

*G*over G. We will redefine this representation as in the following.

How to cite this paper: Wazzan, S.A. and Saleh, A. (2019) On the First and Second Locating Zagreb Indices of Graphs. Applied Mathematics, 10, 805-816.

https://doi.org/10.4236/am.2019.1010057

Received: September 7, 2019 Accepted: September 24, 2019 Published: September 27, 2019

Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0).

http://creativecommons.org/licenses/by/4.0/

DOI: 10.4236/am.2019.1010057 806 Applied Mathematics

Definition 1 ([18]) Let *G*=

### (

*V E*,

### )

_{ be a connected graph with vertex set }

### {

1, , ,2*n*

### }

*V* = *v v* _{} *v* _{. A locating function of G denoted by }**L**

### ( )

*G*is a function

### ( ) ( )

*G V G*:

_{→}

### (

+### { }

0### )

*n*

**L** such that

### ( )

*vi*=

*=*

**v**i### (

*d v v d v v*

### (

1, ,*i*

### ) (

2, , ,*i*

### )

*d v v*

### (

*n*,

*i*

### )

### )

**L** , where *d v v*

### (

*i*,

*j*

### )

is the distance between the vertices*vi*and

*vj*in G. The vector

*is called the locating vector corresponding to the vertex*

**v**i*vi*, where

*⋅*

**v v**i*j*is actually the dot product of the vectors

*and*

**v**i*in the integers space*

**v**j### (

### { }

0### )

*n*
+

such that *vi* is
adjacent to *vj*.

The above locating function and huge applications of Zagreb indices moti-vated us to introduce two new topological indices, namely first and second lo-cating indices, based on the locating vectors.

Definition 2. Let *G*=

### (

*V E*,

### )

_{ be a connected graph with a vertex set }

### {

1, , ,2*n*

### }

*V* = *v v* *v* and an edge set *E G*

### ( )

. Then we define the first and second locating indices as### ( )

( )

### ( )

### ( )

( )2

1 and 2 ,

*i* *i j*

*i* *i* *j*

*v V G* *v v E G*

*M G* *M G*

∈ ∈

=

### ∑

*=*

**v**### ∑

*⋅*

**v v**

respectively.

All graphs in this paper will be assumed simple, undirected and connected unless stated otherwise. For graph theoretical terminologies, we refer [19] to the readers.

**2. Some Exact Values in Terms of Locating Indices **

In this section, by considering Definition 2, we determine the first and second
locating indices for the standard graphs *Kn*, *Cn*, *Kn m*, , *Wn*, *Pn*, and also for

the join graph *G G G*≅ 1+ 2 such that *G*1 and *G*2 are both connected graphs

with diameter 2 and G will be assumed as *C*3, *C*5-free graphs.

Theorem 3. Let *G K*≅ *n* be the complete graph with a vertex set

### ( ) {

1, , ,2*n*

### }

*V G* = *v v* _{} *v* _{,}_{ where } *n*≥2_{. Then } *M K*_{1}

### ( )

*n*=

*n n*

### (

−1### )

and### ( )

### (

### )(

### )

2

1 2

2
*n*

*n n* *n*

*M K* = − − _{.}

Proof. Let * vi* be a locating vector corresponding to the vertex

*v V Gi*∈

### ( )

. Then*=*

**v**i### (

*a a*1, , ,2

*an*

### )

such that*ai*=0 and

*ai*+1=1. Thus

### ( )

2

1
*i* = −*n*

* v* .

But we have total n vertices in *V G*

### ( )

, and so*M K*1

### ( )

*n*=

*n n*

### (

−1### )

, as required.On the other hand, for any two locating vectors * vi* and

*, where*

**v**j*i*≠

*j*, we

definitely have * v vi*⋅

*j*= −

*n*2. Hence 2

### ( )

### (

### )(

### )

1 2

2
*n*

*n n* *n*

*M K* = − − _{.}_{}

In the next two Theorems, we investigate the cycle *Cn* depends on the status

of n.

Theorem 4. For an even integer *n*≥2, let *G C*≅ *n*. Then

### ( )

### (

2### )

1

2
12
*n*

*n n*

*M C* = + _{ and }

### ( )

### (

### )

2 2

2

2
12
*n*

*n n*

*M C* = − _{.}

DOI: 10.4236/am.2019.1010057 807 Applied Mathematics

1=0,1,2,3, , ,_{2 2}*n n*−1,_{2}*n*−2, ,1 ,

* v*

2=1,0,1,2, ,_{2}*n*−1, ,*n n*_{2 2}−1, ,2 ,

* v*

3 =2,1,0,1, ,_{2}*n*−2,*n*_{2}−1, , ,3 ,*n*_{2}

* v*

1,2,3, , , 1, 2, 2, ,0 ,

2 2 2 2

*n* = *n n*− *n*− *n*−

* v*

and hence 2 2 2 2

1

2

4
*n*

*i* *i*

*n*
*i*
=

=

### ∑

−* v* . It is not difficult to see that each

*has the same*

**v**icomponents within different location, and so each 2

*i*

* v* has the same sum as the

form of 2

### (

1### )(

2 3### )

212
*i*

*n n*+ *n*+ − *n*
=

* v* . Therefore

### ( )

### (

### )

2

1

2
12
*n*

*n n*

*M C* = + _{. In }

addi-tion, by the symmetry,

### ( )

### (

### )

### (

### )

22 1

2

1 1 1 _{2}

2 2 2 2

2 1 2 1 2 1

6 2 12

*n*

*i* *i*
*i*

*n n* _{n}*n n*

*n n*
*i i*

+ =

_{+} _{+} _{+}

_{} _{} _{} _{} _{−}

⋅ = − = − − − =

### ∑

**v v**

which gives

### ( )

### (

### )

2 2

2

2
12
*n*

*n n*

*M C* = − _{.}_{}

Theorem 5. For an odd integer *n*≥3, let *G C*≅ *n*. Then

### ( )

2### (

2### )

1

1
12
*n*

*n n*

*M C* = − _{ and }

### ( )

### (

### )(

### )(

### )

2

1 2 3

12
*n*

*n n* *n* *n*

*M C* = − − + _{.}

Proof. With a similar procedure as in the proof of Theorem 4, we get

1 0,1,2,3, ,*n*_{2}1,*n*_{2}1 1,*n*_{2}1 2, ,1 ,

− − −

=_{} − − _{}

* v*

2 1,0,1,2, ,*n*_{2}1 1,*n*_{2}1,*n*_{2}1 1, ,2 ,

− − −

=_{} − − _{}

* v*

3 2,1,0,1, ,*n*_{2}1 2,*n*_{2}1 1,*n*_{2}1, ,3 ,

− − −

=_{} − − _{}

* v*

1 1 1

1,2,3, , , 1, 2, ,0

2 2 2

*n* *n* *n* *n*

− − −

=_{} − − _{}

* v*

which implies

### (

### )

1

2 2

2 2

1

1

2 ,

12
*n*

*i*
*i*

*n n*
*i*

− =

− =

### ∑

=**v**

and so

### ( )

### (

### )

2 2

1

1
12
*n*

*n n*

DOI: 10.4236/am.2019.1010057 808 Applied Mathematics

### (

### ) (

### )

### (

### )

### (

### )(

### )(

### )

1

2 2

1 2

2

1

2 1

4

1 1 _{1 2} 1 _{1} 1 1 _{1}

1

2 2 2 2 2

2 1 2 1

6 2 4

1 2 3

12
*n*

*i* *i*
*i*

*n*
*i i*

*n* *n* *n* *n* *n*

*n*

*n* *n* *n*

− +

=

− ⋅ = − +

− − _{+} − _{+} − − _{+}

_{} _{} _{} _{} _{} _{−}

= − − − +

− − + =

### ∑

**v v**

which gives the exact value of *M C*2

### ( )

*n*as depicted in the statement of

theo-rem.

Now we will take into account the complete bipartite graphs to determine the locating indices.

Theorem 6. Let *G K*≅ *n m*, , where 1≤ ≤*n m*. Then

### (

### )

### (

2 2### )

### (

### )

1 *n m*, 4 4 2

*M K* = *n* +*m* − *n m*+ + *nm*_{ and }

### (

### )

### (

### )

2 *n m*, 2 2

*M K* = *nm n m*+ − _{.}

Proof. For all 1≤ ≤*i n* and 1≤ ≤*j m*, by labeling the adjacent vertices *vi*

and *vn j*+ of *Kn m*, , the locating vectors * vi* of

*vi*are given by:

1 2

1 2

3 1

3

1

0,2, ,2,1,1, ,1 , 2,0,2, ,2,1,1, ,1 ,

2,2,0,2, ,2,1,1, ,1 , , 2, ,2,0,1,1, ,1 ,

1, ,1,0,2

*n* *m* *n* *m*

*n* *m* *n* *m*

*n*

*n*
*n*

− −

− −

+

=_{} _{} =_{} _{}

=_{} _{} =_{} _{}

=

**v****v**

**v****v**

**v**

1 2

2

1

,2, ,2 , 1, ,1,2,0,2, ,2 , ,

1, ,1,2, ,2,0 .

*m* *n* *m*

*n*

*n* *m*

*n m*

− −

+ −

+

=

= _{} _{}

**v**

**v**

In here, for any *i*=1, 2, , *n* , we have 2 _{4}

### (

_{1}

### )

*i* = *n*− +*m*

* v* and for any

1, 2, ,

*i n*= + *n*+ *n m*+ , we get * vi*2 =4

### (

*m*− +1

### )

*n*. Therefore

### (

### )

### (

### (

### )

### )

### (

### (

### )

### )

### (

### )

### (

### )

1 ,

2 2

4 1 4 1

4 4 2 .

*n m*

*M K* *n* *n* *m m* *m* *n*

*n* *m* *n m* *nm*

= − + + − +

= + − + +

On the other hand, for any two consecutive locating vertices * v vi*,

*i*+1 in

*Kn m*, ,

since * v vi*⋅

*i*+1=2

### (

*n m*+ −2

### )

, we obtain*M K*2

### (

*n m*,

### )

=2*nm n m*

### (

+ −2### )

.Since the following consequences of Theorem 6 are very special cases and clear, we will omit their proofs.

Corollary 7. Let *G K*≅ *n n*, , where *n*≥1. Then *M K*1

### ( )

*n n*, =2 5

*n n*

### (

−4### )

and### ( )

2### (

### )

2 *n n*, 2 2 2

*M K* = *n* *n*− _{.}

Corollary 8. Let *G K*≅ 1,*m*. Then *M K*1

### ( )

1,*m*=2 2

*m m*

### (

−1### )

and### ( )

### (

### )

2 1,*m* 2 1

*M K* = *m m*− _{.}

The case for wheel graphs will be investigated in the following result.

Theorem 9. Let us consider G as the wheel graph *Wn* (*n*≥4) with *n*+1
vertices. Then we have *M W*1

### ( )

*n*=4

*n n*

### (

−2### )

and*M W*2

### ( )

*n*=

*n n*

### (

6 15−### )

.DOI: 10.4236/am.2019.1010057 809 Applied Mathematics

vertices of *V G*

### ( )

in the anticlockwise direction as*v v*1, , , ,2

*v vn*

*n*+1 such that 1

*n*

*v* + is the center of the wheel, we obtain

3 3

1 2

2 3

3

1

0,1,2,2, ,2,1,1 , 1,0,1,2,2, ,2,1 ,

2,1,0,1,2, ,2,1 , , 1,2,2, ,2,1,0,1 ,

1,1, ,1,0 .

*n* *n*

*n* *n*

*n*

*n*
*n*

− −

− −

+

=_{} _{} =_{} _{}

=_{} _{} =_{} _{}

= _{} _{}

**v****v**

**v****v**

**v**

Now for any locating vector * vi* corresponding to a vertex

*vi*

### (

*i*∈

### {

1,2, ,*n*

### }

### )

,we have 2 _{4} _{9}

*i* = *n*+

* v* and 2

1

*n*+ =*n*

* v* . Hence

*M W*1

### ( )

*n*=4

*n n*

### (

−2### )

.For *M W*2

### ( )

*n*, by labeling the vertices as above, we have

1 2

3 3

3 4

2 1

5

3

, ,2,2, ,2,1, , , , ,2,2, ,2,1 ,

2, , , ,2, ,2,1 , 2,2, , , ,2, ,2,1 ,

2,2,2, , , ,2, ,2,1 , , 1,2,2, ,2, ,

*n* *n*

*n* *n*

*n*

*n* *n*

− −

− −

−

=_{} _{} =_{} _{}

=_{} _{} =_{} _{}

=_{} _{} =

**v****v**

**v****v**

**v****v**

**0 1** **1** **1 0 1**

**1 0 1** **1 0 1**

**1 0 1** **1**

1

, ,

1,1, ,1,0 .
*n*

*n*
+

=

**v**_{}_{}

**0 1**

Bearing in mind the permutation of components **1 0 1**, , in each vector * vi*,

where *i*=1, 2, , *n*, it is easy to see that any two adjacent vertices *vi* and *vj*

### {

### }

### (

*i j*, ∈ 1,2, ,

*n*

### )

satisfy*⋅*

**v v**i*j*=4 11

*n*− and

*⋅*

**v v**i*i*+1=2

*n*−4 for

1, 2, ,

*i*= *n*. Hence *M W*2

### ( )

*n*=

*n n*

### (

6 15−### )

.The result for determining of locating indices on path graphs can be given as in the following.

Theorem 10. Let *G P*≅ *n*

### (

*n*≥3

### )

. Then### ( )

1### (

### )(

### )(

### )

1

1

1 2 2 1 , 3

*n*
*n*

*j*

*n j n j* *n* *j*

*M P* −

=

− − + − + =

### ∑

and

### ( )

1### (

### )(

### )(

### )

2

1

1 1

2 .

3
*n*

*n*
*j*

*n j n j* *n j*

*M P* −

=

− − + − − =

### ∑

Proof. Assume that G is the graph *Pn* (*n*≥3). By labeling the vertices from

left to right as *v v*1, , ,2 *vn* according to the locating function, the

correspond-ing vector for each vertex *v V Gi*∈

### ( )

(*i*=1, ,

*n*) will be the form of

### (

### )

### (

### )

### (

### )

### (

### )

1 2

1

0,1,2,3, , 1 , 1,0,1,2, , 2 , , 2, 1, ,0,1 , 1, 2, 3, ,0 .

*n* *n*

*n* *n*

*n* *n* *n* *n* *n*

−

= − = −

= − − = − − −

**v****v**

**v****v**

By applying the symmetry on components between the vector pairs * v v*1,

*n*

DOI: 10.4236/am.2019.1010057 810 Applied Mathematics

### ( )

1 2 1### (

### )(

### )(

### )

1

1 1 1

1 2 2 1

2 .

3
*n j*

*n* *n*

*n*

*j* *i* *j*

*n j n j* *n* *j*

*M P* − −*i* −

= = =

− − + − + =

### ∑∑

=### ∑

For *M P*2

### ( )

*n*, we see that

### ( ) ( )

### (

### )(

### )

1### (

### )

1 2

1

0 1 1 0 1 2 *n* 1 ,

*i*

*n* *n* −*i i*

=

⋅ = ⋅ + ⋅ + + − − =

### ∑

−* v v*

### ( ) ( )

### (

### )(

### )

1### (

### )

2 3

1

1 2 0 1 2 3 *n* 1 ,

*i*

*n* *n* −*i i*

=

⋅ = ⋅ + ⋅ + + − − =

### ∑

−* v v*

### (

### )

1

3 4

1 1 ,

*n*

*i* *i i*
−

=

⋅ =

### ∑

−**v v**

However, by the symmetry between the components of the vectors as men-tioned above, we get

### ( )

1### (

### )

1 2 21 1 1 1 1

2*n* *n j* 1 2*n* *n j* *n j*
*n*

*j* *i* *j* *i* *i*

*M P* − − *i i* − − *i* −*i*

= = = = =

= − = _{} − _{}

### ∑∑

### ∑ ∑ ∑

which can be rewritten as in the form

### ( )

### (

### )(

### )(

### ) (

### )(

### )

### (

### )(

### )(

### )

1 2

1 1

1

1 2 2 1 1

2

6 2

1 1

2 .

3
*n*

*n*
*j*
*n*

*j*

*n j n j* *n* *j* *n j n j*

*M P*

*n j n j* *n j*
−

=

−

=

− − + − + − − +

= _{} − _{}

− − + − −

=

### ∑

### ∑

This complete the proof.

It is known that from the elementary textbooks the join *G G G*= 1+ 2 of

graphs *G*1 and *G*2 with disjoint vertex sets *V*1 and *V*2 and edge sets *E*1

and *E*2 is the graph union *G G*1 2 together with all the edges joining *V*1 and
2

*V* . In the following theorem we find first and second locating indices for the
join graph G.

Theorem 11. Let *G G G*≅ 1+ 2 such that *G*1 and *G*2 are both connected

graphs with diameter 2 and G is a *C*3 or *C*5-free graph. Assume that *G*1 has
1

*n* vertices and *m*1 edges while *G*2 has *n*2 vertices and *m*2 edges. Then

### ( )

### (

2 2### )

### (

### )

1 2 1 2 4 1 2 1 2 6 1 2 ,

*M G* = *n n* + *n* +*n* − −*n n* − *m m*+

and

### ( )

### (

### ) (

### )

### (

### )

2 2 1 1 2 2 4 1 2 2 1 2 1 2 2 .

*M G* = *m n m n*+ − *m m*+ + *n n n n*+ −

Proof. Assume that G satisfies the conditions in the statement of theorem. Let us label the vertices of the graph G as

1 1 1 1 2

1, , , ,2 *n* *n* 1, *n* 2, , *n n* ,
*v v* *v v* + *v* + *v* +

where *v v*1, , ,2 *vn*_{1}∈*V G*

### ( )

1 and*vn*1+1,

*vn*1+2, ,

*vn n*1+2∈

*V G*

### ( )

2 . Also let**v**

be
**v**

the locating vector corresponding to the vertex v such that *v V G*∈

### ( )

1 :( ) ( )

deg _{1} deg 1 _{2}

0,1, ,1, 2, ,2 ,1, ,1 .
*n*
*v* *n*− *v*−

=

DOI: 10.4236/am.2019.1010057 811 Applied Mathematics

Then 2

### ( )

2 4 1 4 3deg

*n* *n* *v*

= + − −

* v* .

Similarly, for any vertex *w V G*∈

### ( )

2 , the locating vector**w**

corresponding to
**w**

w:

( )

( )

1 deg 2 deg 1 1, ,1,0,1, ,1, 2, ,2 .

*n* *w* *n* − *w*−

=

* w*

_{}

So 2

### ( )

1 4 2 4 3deg

*n* *n* *w*

= + − −

* w* . Therefore, by the above equalities on

*2*

_{v}and *_{w}*2

_{, we obtain }

### ( )

### (

### )

### (

### )

### (

### )

### (

### )

1 1 2 1 1 2 1 2 2

2 2

1 2 1 2 1 2 1 2

4 4 6 4 4 6

2 4 6 .

*M G* *n n* *n* *m n n* *n* *m*

*n n* *n* *n* *n n* *m m*

= + − − + + − − = + + − − − +

Now, let us make partition to the set of vertices of G as

### ( )

### {

: , 1### }

,*A*= *u v u v V G*⋅ ∈

### ( )

### {

: , 2### }

,*B*= *u v u v V G*⋅ ∈

### ( )

### ( )

### {

: 1 , 2### }

.*C*= *u v u V G v V G*⋅ ∈ ∈

Hence *M G*2

### ( )

can be written as### ∑

*u v A*⋅ ∈

*⋅ +*

**u v**### ∑

*u v B*⋅ ∈

*⋅ +*

**u v**### ∑

*u v C*⋅ ∈

*⋅ . To get*

**u v**### ∑

*u v A*⋅ ∈

*⋅ for any two adjacent vertices*

**u v***u v V G*, ∈

### ( )

1 , let us consider( )

( ) 2

1

deg deg 1

0,1, ,1, 2, ,2 ,1, ,1
*n*
*u* *n*− *u*−

=

* u*

_{}

( ) 1 deg( )1 2

deg 1

1,0,2, ,2, 1, ,1 ,1, ,1 .
*n*

*n* *u*

*u*− − −

=

**v**_{}

We then have

### ( )

### (

### )

### (

1### ( )

### )

2 2 12 deg *u* 1 2 *n* deg *u* 1 *n* *n* 2*n* 4
⋅ = − + − − + = + −

**u v**

which implies

### ∑

*u v A*⋅ ∈

*⋅ =*

**u v***m n*1

### (

2+2*n*1−4

### )

. With a similar calculation, we get### (

### )

2 1 2 2 4

*u v B*⋅ ∈ ⋅ =*m n* + *n* −

### ∑

*.*

**u v**Next, we need to calculate

### ∑

*⋅ ∈*

_{u v C}*⋅ . To do that let us take*

**u v***u V G*∈

### ( )

1 and### ( )

2*v V G*∈ _{, and then labeling as }

( )

( ) 2

1

deg deg 1

0,1, ,1, 2, ,2 ,1, ,1
*n*
*u* *n*− *u*−

=

* u*

_{}

( )

( )

( )

( )

1 2

deg 1 deg 1 deg deg 1

1, ,1, 1, ,1 ,0,1, ,1, 2, ,2 .
*u*+ *n*− *u*− *v* *n* − *v*−

=

* v*

_{}

Hence we get

### ( )

### (

### ( )

### )

### ( )

### (

### ( )

### )

### (

1 2### )

1### (

### ( )

### ( )

### )

2deg 2 deg 1 deg 2 deg 1

2 4 deg deg

*u* *n* *u* *v* *n* *v*

*n n* *u* *v*

⋅ = + − − + + − − = + − − −

**u v**

DOI: 10.4236/am.2019.1010057 812 Applied Mathematics

After all above calculations, we finally obtain

### ( )

### (

### )

### (

### )

### (

### )

### (

### )

### (

### ) (

### )

### (

### )

2 1 2 1 2 1 2

1 2 1 2 2 1 1 2

1 1 2 2 1 2 1 2 1 2

2 4 2 4

2 4 2 2

2 4 2 2 .

*M G* *m n* *n* *m n* *n*

*n n* *n n* *n m* *n m*

*m n m n* *m m* *n n n n*

= + − + + − + + − − −

= + − + + + −

Hence the result.

**3. Locating Indices of Firefly Graphs **

We recall that a firefly graph *Fs t n s t*, , 2 2 1− − − (*s*≥0,*t*≥0 and *n*−2*s*− − ≥2 1 0*t* )

is a graph of order n that consists of s triangles, t pendant paths of length 2 and

2 2 1

*n*− *s*− −*t* pendent edges that are sharing a common vertex (cf. [20]). Let

*n*

be the set of all firefly graphs *Fs t n s t*, , 2 2 1− − − . Note that *n* contains the stars

### (

0,0, 1### )

*n* *n*

*S* ≅*F* − , stretched stars

### (

≅*F*0, , 2 1

*t n t*− −

### )

, friendship graphs_{1,0,0}

2

*n*

*F*−

≅

and

butterfly graphs

### (

≅*Fs n s*,0, 2 1− −

### )

.In the next theorem we present the first and second locating indices for the
firefly graph. In our calculations, for simplicity, we denote *n*−2*s*− −2 1*t* _{ by a }
single letter l.

Theorem 12. Let *G F*≅ *s t l*, , (*s*≥0,*t*≥0 and *l*≥0) be a firefly graph of

or-der n. Then

### ( )

2 2 21 4 16 26 2 16 52 10 38 28 ,

*M G* = *l* + *ls*+ *lt*− +*l* *s* + *st*− *s*+ *t* − *t*

and

### ( )

2 2 22 2 16 13 2 24 52 20 22 17 .

*M G* = *l* + *ls*+ *lt*− +*l* *s* + *st*− *s*+ *t* − *t*

Proof. Let *G F*≅ *s t l*, , (*s*≥0,*t*≥0 and *l*≥0) is a firefly graph of order n. Let

us label the vertices with clockwise direction as

1 2 2 1 2 2 2 3 2 1 2 2

2 3 2 1 2 2 2 3 2 2 1

, , , , , , , , ,

, , , , , , ,

*s* *s* *s* *s l* *s l*

*s l* *s l t* *s l t* *s l t* *s t l*

*v v* *v* *v* *v* *v* *v*

*v* *v* *v* *v* *v*

+ + + + + + + + + + + + + + + + + + + + +

where *v*1 is the center of the firefly graph and

2 3 2 1

2

, , , * _{s}* : vertices of triangles,

*s*

*v v*_{} *v* +_{}

2 2*s* , 2 3*s* , , 2*s l* 1: vertices of pendent edges,

*l*

*v*_{}+ *v* + *v* + +

2*s l* 2, 2*s l* 3, , 2*s l t*1: vertices of pendent path of length 1,

*t*

*v*_{}+ + *v* + + *v* + + +_{}

2*s l t* 2, 2*s l t* 3, , 2 2*s t l*1: vertices of pendent path of length 2.

*t*

*v*_{}+ + + *v* + + + *v* + + +

Now we calculate the corresponding vectors * vi* for each vertex

*v V Gi*∈

### ( )

, where*i*=1,2, ,2

*s*+2

*t l*+ +1, as in the following:

1

2

0,1,1, ,1,1,1, ,1,1,1, ,1,2,2, ,2 ,

*s* *l* *t* *t*

=

**v**_{}_{}_{ }_{}_{ }_{}_{ }

2

2 2

1,0,1,2,2, ,2,2,2, ,2,2,2, ,2,3,3, ,3 ,

*s*− *l* *t* *t*

=

DOI: 10.4236/am.2019.1010057 813 Applied Mathematics

3

2 2

1,1,0,2,2, ,2,2,2, ,2,2,2, ,2,3,3, ,3 ,

*s*− *l* *t* *t*

=

**v**_{ }

4

2 4

1,2,2,0,1,2,2, ,2,2,2, ,2,2,2, ,2,3,3, ,3 ,

*s*− *l* *t* *t*

=

**v**_{ }

5

2 4

1,2,2,1,0,2,2, ,2,2,2, ,2,2,2, ,2,3,3, ,3 ,

*s*− *l* *t* *t*

=

**v**_{ }

2 1

2 2

1,2,2, ,2,1,0,2,2, ,2,2,2, ,2,3,3, ,3 ,
*s*

*s* *l* *t* *t*

+

−

=

**v**_{} _{ }

2 2

2 1

1,2,2, ,2,0,2,2, ,2,2,2, ,2,3,3, ,3 ,
*s*

*s* *l* *t* *t*

+

−

=

**v**_{} _{ }

2 3

2 2

1,2,2, ,2,2,0,2,2, ,2,2,2, ,2,3,3, ,3 ,
*s*

*s* *l* *t* *t*

+

−

=

**v**_{} _{ }

2 1

2 1

1,2,2, ,2,2,2, ,2,0,2,2, ,2,3,3, ,3
*s l*

*s* *l* *t* *t*

+ +

−

=

**v**

2 2

2 1 1

1,2,2, ,2,2,2, ,2,0,2,2, ,2,1,3,3, ,3
*s l*

*s* *l* *t* *t*

+ +

− −

=

**v**

2 1

2 1 1

1,2,2, ,2,2,2, ,2,2,2, ,2,0,3,3, ,3,1 ,
*s l t*

*s* *l* *t* *t*

+ + +

− −

=

**v**

2 2

2 1 1

2,3,3, ,3,3,3, ,3,1,3,3, ,3,0,4,4, ,4 ,
*s l t*

*s* *l* *t* *t*

+ + +

− −

=

**v**

2 3

2 2 2

2,3,3, ,3,3,3, ,3,3,1,3,3, ,3,0,4,4, ,4 ,
*s l t*

*s* *l* *t* *t*

+ + +

− −

=

**v**

2 2 1

2 1 1

2,3,3, ,3,3,3, ,3,3,3, ,3,1,4,4, ,4,0 .
*s l t*

*s* *l* *t* *t*

+ + +

− −

=

**v**

Suppose that *A B C D V G*, , , ⊂

### ( )

_{ such that }

### {

### }

### {

### }

### {

2 22 3 2 32 1 2 1### }

2 2### {

22 32 2 2 31 2 2 1### }

, , , , , , , ,

, , , , , , , .

*s* *s l* *s l* *s l t*

*s* *s* *s l* *s l t* *s l t* *s t l*

*A* *v v* *v* *C* *v* *v* *v*

*B* *v* *v* *v* *D* *v* *v* *v*

+ + + + + + + +

+ + + + + + + + + + + + +

= =

= =

Therefore we can write

### ( )

2 2 2 21 .

*v A* *v B* *v C* *v D*

*M G*

∈ ∈ ∈ ∈

=

### ∑

*+*

**v**### ∑

*+*

**v**### ∑

*+*

**v**### ∑

**v**

For the calculation of 2

*v A*∈

### ∑

*, we have the cases 2*

**v**1 =2*s l t*+ + +4*t*=2*s l*+ +5*t*

**v**

DOI: 10.4236/am.2019.1010057 814 Applied Mathematics

### (

### )

2 _{2 4 2} _{2 4 4 9} _{4 8 13 6,}

*i* = + *s*− + + + = + +*l* *t* *t* *l* *s* *t*−

**v**

where *i*=2,3, , 2 *s*+1. Hence

### (

### )

2

2

2

2 5 2 4 8 13 6

2 5 8 16 26 12

10 5 8 26 16 .

*v A* *s l* *t* *s l* *s* *t*

*s l* *t* *sl* *s* *st* *s*

*l* *s* *t* *ls* *st* *s*

∈

= + + + + + −

= + + + + + −

= − + + + +

### ∑

**v**On the other hand, for the calculation of 2

*v B*∈

### ∑

*, we have*

**v**### ( ) (

### )

2 _{1 4 2} _{4} _{1 4 9} _{4 8 13 3,}

*i* = + *s* + *l*− + + =*t* *t* *l*+ *s*+ *t*−

**v**

where for *i*=2 1,2*s*+ *s*+2, ,2 *s l*+ +1. Thus

### (

### )

2 _{4 8 13 3} _{4}2 _{8} _{13} _{3 .}

*v B*∈ *l l* *s* *t* *l* *ls* *lt* *l*

= + + − = + + −

### ∑

**v**Thirdly to calculate 2

*v C*∈

### ∑

*, we have*

**v**### ( )

### (

### ) (

### )

2 _{2 4 2} _{4 4} _{1 9} _{1} _{4 8 13 11,}

*i* = + *s* + +*l* *t*− + *t*− = *l*+ *s*+ *t*−

**v**

where *i*=2*s l*+ +2,1,2*s l*+ +3, ,2 *s l t*+ + +1, and so

### (

### )

2 _{4 8 13 11} _{4} _{8} _{13}2 _{11 .}

*v C*∈ *t l* *s* *t* *tl* *ts* *t* *t*

= + + − = + + −

### ∑

**v**Finally, for the case of 2

*v D*∈

### ∑

*, we get*

**v**### ( )

### (

### )

### (

### )

2 _{3 9 2} _{9 9} _{1 16} _{1 9 18} _{25 22,}

*i* = + *s* + +*l* *t*− + *t*− = +*l* *s*+ *t*−

**v**

where *i v*= 2*s l t*+ + +2,*v*2*s l t*+ + +3, , *v*2 2*s t l*+ + +1. This gives

### (

### )

2 _{9 18} _{25 22} _{9} _{18} _{25}2 _{22 .}

*v D*∈ *t l* *s* *t* *tl* *ts* *t* *t*

= + + − = + + −

### ∑

**v**By collecting all above calculations, we obtain

### ( )

2 2 2 2 12 2

2 2

2 2 2

10 5 8 26 16 4 8 13 3

4 8 13 11 9 18 25 22
4 16 26 2 16 52 10 38 28 ,
*v A* *v B* *v C* *v D*

*M G*

*l* *s* *t* *ls* *st* *s* *l* *ls* *lt* *l*

*tl* *ts* *t* *t* *tl* *ts* *t* *t*

*l* *ls* *lt* *l* *s* *st* *s* *t* *t*

∈ ∈ ∈ ∈

= + + +

= − + + + + + + + − + + + − + + + − = + + − + + − + −

### ∑

**v**### ∑

**v**### ∑

**v**### ∑

**v**

as required.

Before starting to calculate the index *M G*2

### ( )

=### ∑

*v u E G*∈

_{i j}_{( )}

*⋅*

**v u**i*j*

_{, we should }

remind that for any two adjacent vertices u and v will be denoted by

*u v*

### ≈

_{. Now, }

let us again consider the same subsets A, B, C and D of *V G*

### ( )

. Therefore we firstly have### (

### )

### (

### )

### (

### )

1

2

2 1 2 2 2 3 2 2 4 5 3

4 8 10 6 .

*i*
*i*

*v A* *s* *s* *l t* *t* *s l* *s* *t*

*sl* *s* *st* *s*

∈

⋅ = + − + + + = + + −

= + + −

### ∑

**v v**### (

### )

### (

### )

### (

### )

1

2

2 2 1 3 2 4 5 2

2 4 5 2 .

*i*
*i*

*v B* *l* *s l* *t* *t* *l l* *s* *t*

*l* *sl* *lt* *l*
∈

⋅ = + − + + = + + −

= + + −

### ∑

**v v**### (

### )

### (

### )

### (

### )

1

2

1 2 2 1 2 2 4 4 1

2 4 4 .

*i*
*i*

*v C* *t* *s l t* *t* *t l* *s* *t*

*tl* *ts* *t* *t*
∈

⋅ = + + + − + = + + −

= + + −

DOI: 10.4236/am.2019.1010057 815 Applied Mathematics

Secondly,

{ }1

### (

### (

### )

### )

### (

### )

1

1

2

2 1 4 2 2 9 2 4 8 13 7

8 16 26 14 .

*i*
*i* *i*

*i* *i*
*v A v*

*v v*

*s* *s* *l t* *t* *s l* *s* *t*

*sl* *s* *st* *s*

+

+ ∈ −

≈

⋅ = + − + + + = + + −

= + + −

### ∑

**v v**Thirdly,

### (

### )

### (

### )

### (

### )

### (

### )

,

2

2 6 2 1 12 1

6 12 18 16 6 12 18 16 .

*i* *i t*
*i* *i t*

*i* *i t*
*v C v* *D*

*v v*

*t* *s l t* *t*

*t l* *s* *t* *tl* *ts* *t* *t*

+ +

+ ∈ ∈

≈

⋅ = + + + − + −

= + + − = + + −

### ∑

**v v**Again, by collecting all above calculations, we obtain

### ( )

{ }1 1

2 1 1 1 1

,

2 2 2

2 2

2 2

4 8 10 6 2 4 5 2 2 4 4

8 16 26 14 6 12 18 16 2 16 13 2 24 52 20

*i* *i t*

*i*

*i* *i* *i*

*i* *i t*
*i* *i*

*i* *i* *i* *i* *i* *i* *i t*

*u C v* *D*
*v A v*

*v A* *v B* *v C*

*v v*
*v v*

*M G*

*sl* *s* *st* *s* *l* *sl* *lt* *l* *tl* *ts* *t* *t*

*sl* *s* *st* *s* *tl* *ts* *t* *t*

*l* *ls* *lt* *l* *s* *st* *s*

+ + +

+ +

∈ ∈ ∈ −

∈ ∈ ∈

≈ ≈

= ⋅ + ⋅ + ⋅ + ⋅ + ⋅

= + + − + + + − + + + − + + + − + + + −

= + + − + + − +

### ∑

**v v**### ∑

**v v**### ∑

**v v**### ∑

**v v**### ∑

**v v**

2

22*t* −17 .*t*

These all above processes complete the proof. Corollary 13. 1) For any friendship graph of order n,

### ( )

2### ( )

21 4 13 9 and 2 6 22 16.

*M G* = *n* − *n*+ *M G* = *n* − *n*+

2) For any butterfly graph of order n,

### ( )

2### ( )

21 4 10 6 6 and 2 8 24 6 2 4.

*M G* = *n* − *n*− *s*+ *M G* = *ns*− *s*− *n*+ *n* +

**4. Conclusion **

In this paper, two new topological indices based on Zagreb indices are proposed. The exact values of these new topological indices are calculated for some stan-dard graphs and for the firefly graphs. These new indices can be used to investi-gate the chemical properties for some chemical compound such as drugs, bridge molecular graph etc. For the future work, instead of defining these new topolog-ical indices based on the degrees of the vertices, we can redefine them based on the degrees of the edges by defining them on the line graph of any graph. Similar calculations can be computed to indicate different properties of the graph.

**Conflicts of Interest **

The authors declare no conflicts of interest regarding the publication of this pa-per.

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