Abstract
Sierpiński graphs are family of fractal nature graphs having applications in mathematics of Tower of Hanoi, topology, computer science, and many more diverse areas of science and technology. This family of graphs can be generated by taking certain number of copies of the same basic graph. A topological index is the number which shows some basic properties of the chemical structures. This article deals with degree based topological indices of uniform subdivision of the generalized Sierpiński graphs S(n,G) and Sierpiński gasket Sn. The closed formulae for the computation of different kinds of Zagreb indices, multiple Zagreb indices, reduced Zagreb indices, augmented Zagreb indices, Narumi-Katayama index, forgotten index, and Zagreb polynomials have been presented for the family of graphs.
1 Introduction
Applications of molecular structure descriptors are a standard procedure in the study of structure–property relations nowadays, especially in the field of QSAR/QSPR study. During the last century, theoretical chemists started working on the use of topological indices to obtain information on various properties of organic substances that depend upon their molecular structure. For this purpose, numerous topological indices were found and studied in the chemical literature (Todeschini and Cansonni, 2008). They used two zeroth order and two first-order connectivity indices for the first time as descriptors in structure–property correlations in an optimization study. A set of new formulas for heat capacity, glass transition temperature, refractive index, cohesive energy, and dielectric constant were introduced – they were based on these descriptors. The Randić index has been used to parallel the boiling point and Kovats constants and was closely correlated with many chemical properties. A graph invariant that correlates the physico-chemical properties of a molecular graph with a number is called a topological index (Hansch and Leo, 1996). The first topological index was introduced by Wiener, a chemist, in 1947 to calculate the boiling points of paraffins in Wiener (1947). Zagreb indices, derived by Gutman and Trinajstić (1972), are used to study molecules and complexity of selected classes of molecules. Zagreb indices have found an interesting use in the QSPR/QSAR modeling and are useful in the study of anti-inflammatory activities of certain chemical instances.
A graph S(n,G) is known as the generalized Sierpiński graph of G of dimension n having vertex set {1,…,l}n and the set {t,s} defines an edge iff ∃i ∈ {1, …, n} such as that:
tj = sj if j < i
ti ≠ si and (ti, s) ∈ E(G)
tj = si and sj = ti if j > i.
Sierpiński graphs appear in many fields of mathematics and other branches of science (Beaudou et al., 2010). One of the most necessary sorts of Sierpiński graphs are the Sierpiński gasket graphs. The Sierpiński gasket graph is outlined as S(n,k) with vertex set (1,2, 3…,n) and there is an edge between 2 vertices x = (x1, x2, x3,…xn) and there is an edge between 2 vertices x = (x1, x2, x3,…xn) and y = (y1, y2, y3,…yn) if and only if there is an h∈[n] such that:
The finite number of iterations in Sierpiński graphs gives Sierpiński gasket graphs and it is denoted by Sn. Sn is consisted of three linked copies of Sn−1 that are up, down left, and downright elements of Sn. These graphs have been given by Scorer et al. (1944). These graphs play a vital role in dynamics system and probability and additionally as in psychological sciences. The generalized Sierpiński graph, S(n,G), is constructed by repeating |G| times S(n − 1,G) and adding one edge between replica i and replica j of S(n − 1,G) wherever pq is an edge of G.
In this paper we will discuss the uniform subdivision of Sn and S(n,G). We will denote subdivision of Sn by SD(Sn) and subdivision of S(n,G) by SD(S(n,G)). We study three types of Sierpiński graphs and now we will calculate the degree based topological indices for these types.
The first and second Zagreb indices which are also known as the graph invariants are the first vertex degree based structures descriptors defined by Gutman and Trinajstić (1972), and elaborated in Gutman et al. (1975) as
and
Here M1(G) and M2(G) are known as the first and second Zagreb index. Gutman, Xu, and Das (Gutman and Das, 2004; Xu and Das, 2012) found the use Zagreb indices in QSPR and in QSAR. These topological indices have been used to study “molecular complexness”, “chirality, ZE-isomorphism”, and Hetro-system. Their chemical applications and mathematical characteristics were studied by Das et al. (2013), Furtula et al. (2010), Gutman (2013, 2014), Nikolic et al. (2003), and Zhou (2004).
The term
Furtula and Gutman (2015) proved that the linear combination of M1 + λF has very accurate mathematical model of some physical properties of alkanes. Caporossi et al. (2010) introduced another index that is called a reduced second Zagreb index. Also this index has very important applications. It is defined as:
Furtula et al. (2010) introduced the augmented Zagreb index in 2010. It is given as:
Furtula et al. (2010) stated that it is a very important index for the study of the heat of formation in octanes and heptanes. If the exponent in AZI is replaces by −0.5 then it will become atom bound connectivity index. The results indicate that the AZI index gives the better results as compare to the ABC index.
Shirdel et al. (2013) gave the third Zagreb index, which is defined as:
This index is combination of F index and second Zagreb index, that is:
By using the above relation, we study the F index with the Zagreb index.
Narumi and Katayama (1984) defined the degree product
Ghorbani and Azimi (2012) introduced the first and second multiple Zagreb indices, which are defines as:
and
The first multiple Zagreb index is square of Narumi-Katayama index.
Fathtabar (2009) defined the first and second Zagreb polynomial of the graph G:
and
where y is an attribute.
For more interesting articles and new developments in the area, please see: Akgunes et al. (2016), Bindusree et al. (2016), Das et al. (2013), Ji et al. (2020), Lokesha et al. (2018), Qu et al. (2019, 2020), and Togan et al. (2020).
In the following section some degree based topological indices for uniform subdivision of Sierpiński like graphs are studied.
2 Zagreb indices and Zagreb polynomials for uniform subdivisions of Sierpiński gasket graphs SD(Sn)
The graphs of uniform subdivision of Sierpiński gasket for 1 ≤ n ≤ 3 is given in Figure 1 and the size of SD(Sn) is 3n. There are 2 types of edges corresponding to the end vertices for n > 1.

Uniform subdivision of Sierpiński gasket graph SD(S1), SD(S2), and SD(S3).
The partition of edge set of SD(Sn) is given in Table 3.1.
where pq ∈ E(G).
The order of the SD(Sn) is
The partition E(G) of SD(Sn)
(dp, dq) | (2,2) | (2,4) |
---|---|---|
Number of edges, |Edp, dq| | 6 | 2(3n) − 6 |
Vertex partition of vertex set of SD(Sn)
dp | 2 | 4 |
---|---|---|
Number of the vertices | 3n + 3 |
|
Theorem 1
The first and second Zagreb indices for G = SD(Sn) is:
Theorem 2
The reduced second Zagreb index for G = SD(Sn) is:
Proof
Using the equation
Theorem 3
The third Zagreb index for G = SD(Sn) is:
Proof
Using the equation
Theorem 4
The F index for G = SD(Sn) is:
Proof
By using the equation F(G) = M3(G) − 2M2(G) and the Table 1 we have:
Theorem 5
The augmented Zagreb index for G = SD(Sn) is:
Proof
Using the equation
Theorem 6
The first and second multiple Zagreb indices for G = SD(Sn) are:
Theorem 7
The Narumi-Katayama index for G = SD(Sn) is:
Proof
Using the equation
Theorem 8
The first Zagreb polynomial for G = SD(Sn) is:
Proof
Using the equation
Theorem 9
The first Zagreb polynomial for G = SD(Sn) is:
Proof
Using the equation
3 Zagreb indices and Zagreb polynomials for uniform subdivisions of Sierpiński gasket graphs for SD(S(n,C3))
The generalized Sierpiński graphs for the SD(S(1,C3)), SD(S(2,C3)), and SD(S(3,C3)) are given in the Figure 2. The size of SD(S(n,C3)) is 3(3n − 1). There are 2 types of edges corresponding to the degrees of end vertices for n > 1. The edge partition for the set of SD(S(n,C3)) is given in the Table 3.

The generalized Sierpiński graphs for the SD(S(1,C3)), SD(S(2,C3)), and SD(S(3,C3)).
The partition of E(G) of SD(S(n,C3))
(dp, dq) | (2,2) | (2,3) |
---|---|---|
Number of edges, |Edp, dp| | 6 | 3n+1 − 9 |
The order of the SD(S(n,C3)) is
Vertex partition of vertex set of SD(S(n,C3))
dp | 2 | 3 |
---|---|---|
Number of the vertices |
|
3n − 3 |
The following theorems represents the formulas for Zagreb indices and Zagreb polynomials for SD(S(n,C3)).
Theorem 10
The first and second Zagreb indices for SD(S(n, C3)) are:
Theorem 11
The reduced second Zagreb index for SD(S(n,C3)) is:
Proof
Using the equation
Theorem 12
The third Zagreb index for SD(S(n,C3)) is:
Proof
Using the equation
Theorem 13
The F index for SD(S(n,C3)) is:
Proof
Using the equation F(G) = M3(G) − 2M2(G) and the Theorem 11 and Theorem 12 we have:
Theorem 14
The augmented Zagreb index for SD(S(n,C3)) is:
Proof
Using the equation
Theorem 15
The first and second multiple Zagreb indices for SD(S(n,C3)) are:
Theorem 16
The Narumi-Katayama index for SD(S(n,C3)) is:
Proof
Using the equation
Theorem 17
The first Zagreb polynomial for SD(S(n,C3)) is:
Proof
Using the equation
Theorem 18
The first Zagreb polynomial for SD(S(n,C3)) is:
Proof
Using the equation
4 Zagreb indices and Zagreb polynomials for uniform subdivisions of Sierpiński gasket graphs for SD(S(n,C4))
The generalized Sierpiński graphs for the SD(S(1,C4)), SD(S(2,C4)), and SD(S(3,C4)) are given in the Figure 3. The size of SD(S(n,C4)) is

The generalized Sierpiński graphs for the SD(S(1,C4)), SD(S(2,C4)), and SD(S(3,C4)).
The partition E(G) of SD(S(n,C4))
(dp, dq) | (2,2) | (2,3) |
---|---|---|
Number of edges, |Edp, dp| |
|
2(4n − 4) |
The order of the S(n,C4) is
The following theorems represent the formulas for Zagreb indices and Zagreb polynomials for SD(S(n,C4)).
Theorem 19
The first and second Zagreb indices for SD(S(n,C4)) are:
Theorem 20
The reduced second Zagreb index for SD(S(n,C4)) is:
Proof
Using the equation
Theorem 21
The third Zagreb index for SD(S(n,C4)) is:
Proof
Using the equation
Theorem 22
The F index for SD(S(n,C4)) is:
Proof
Using the equation F(G) = M3(G) − 2M2(G) and the Theorem 20 and Theorem 21 we have:
Theorem 23
The augmented Zagreb index for SD(S(n,C4)) is:
Proof
Using the equation
Theorem 24
The first and second multiple Zagreb indices for SD(S(n,C4)) are:
Vertex partition of vertex set of SD(S(n,C4))
dp | 2 | 3 |
---|---|---|
Number of the vertices |
|
|
Theorem 25
The Narumi-Katayama index for SD(S(n,C4)) is:
Proof
Using the equation
Theorem 26
The first Zagreb polynomial for SD(S(n,C4)) is:
Proof
Using the equation
Theorem 27
The first Zagreb polynomial for SD(S(n,C4)) is:
Proof
Using the equation
5 Conclusion
Topological indices are often studied with the help of their descriptors. In this paper certain degree based topological indices namely Zagreb indices, multiple Zagreb indices, reduced Zagreb indices, augmented Zagreb indices, Narumi-Katayama index, forgotten index, and Zagreb polynomials have been studied by subdivision of three families of Sierpiński graphs namely SD(Sn),SD(S(n,C3)) and SD(S(n,C4)). In future we will pay attention by subdividing the other families of Sierpiński graphs.
Acknowledgement
The authors are grateful to anonymous referees and editor for their valuable suggestions/criticism which helped us to improve the quality of the paper.
Funding information:
This work is supported in part by the China Postdoctoral Science Foundation under Grant 2017M621579, in part by the Postdoctoral Science Foundation of Jiangsu Province under Grant 1701081B, in part by the Project of Anhui Jianzhu University under Grant 2016QD116. Natural Science Fund of Education Department of Anhui Province under Grant KJ2020A0478.
Author contributions:
Jia-Bau Liu: Project administration, Writing – original draft; Hafiz Muhammad Afzal Siddiqui: Methodology visualization; Muhammad Faisal Nadeem: Formal analysis, Visualization; Muhammad Ahsan Binyamin: Formal analysis, Writing – review and editing.
Conflict of interest:
Authors state no conflict of interest.
Data availability statement:
All data are provided in the manuscript.
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© 2021 Jia-Bao Liu et al., published by De Gruyter
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