OFFSET
0,1
COMMENTS
a(n) is the first Zagreb index of the Wang's helicene-based nanostar DNS[n]. The first Zagreb index of a simple connected graph is the sum of the squared degrees of its vertices. Alternately, it is the sum of the degree sums d(i)+ d(j) over all edges ij of the graph. The pictorial definition of DNS[n] can be viewed in the H. Shabani A. R. et al. reference (it is denoted DNS_{2}[n]).
The M-polynomial of the Wang's helicene-based dendrimer DNS[n] is M(DNS[n],x,y) = (2*2^n - 1)*x*y^3 + (6*2^n -4)*x^2*y^2 + (10*2^n - 12)*x^2*y^3 + (15*2^n - 16)*x^3*y^3.
REFERENCES
H. Shabani, A. R. Ashrafi, and I. Gutman, Geometric-arithmetic index: an algebraic approach, Studia UBB, Chemia, 55, No. 4, 107-112, 2010.
LINKS
E. Deutsch and Sandi Klavzar, M-polynomial and degree-based topological indices, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102.
I. Gutman and K. C. Das, The first Zagreb index 30 years after, MATCH Commun. Math. Comput. Chem. 50, 2004, 83-92.
Index entries for linear recurrences with constant coefficients, signature (3,-2)
FORMULA
G.f.: 4*(-1 + 45*x)/((1 - x)*(1 - 2*x)).
a(n) = 3*a(n-1) - 2*a(n-2).
MAPLE
seq(172*2^n-176, n = 0 .. 35);
CROSSREFS
KEYWORD
sign,easy,changed
AUTHOR
Emeric Deutsch, Nov 13 2016
STATUS
approved