OFFSET
0,1
COMMENTS
a(n) is the second Zagreb index of the dendrimer D[n], defined pictorially in Fig. 1 of the Heydari et al. reference.
The second Zagreb index of a simple connected graph is the sum of the degree products d(i)d(j) over all edges ij of the graph.
The M-polynomial of D[n] is M(D[n]; x, y) = 3*2^n*x*y^3 + 6*x^2*y^3 + 3*(2^n - 1)*x^3*y^3 (n>=0).
LINKS
E. Deutsch and Sandi Klavzar, M-polynomial and degree-based topological indices, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102.
A. Heydari and I. Gutman, On the terminal Wiener index of thorn graphs, Kragujevac J. Sci., 32, 2010, 57-64.
Index entries for linear recurrences with constant coefficients, signature (3,-2).
FORMULA
From Vincenzo Librandi, May 28 2018: (Start)
G.f.: 9*(5 - 6*x)/((1 - 2*x)*(1 - x)).
a(n) = 3*a(n-1) - 2*a(n-2). (End)
a(n) = 9*A000051(n+2). - R. J. Mathar, Jul 22 2022
MAPLE
seq(36*2^n + 9, n = 0..40);
MATHEMATICA
Table[36 2^n + 9, {n, 0, 33}] (* Vincenzo Librandi, May 28 2018 *)
LinearRecurrence[{3, -2}, {45, 81}, 40] (* Harvey P. Dale, Jan 08 2020 *)
PROG
(Magma) [36*2^n+9: n in [0..33]]; // Vincenzo Librandi, May 28 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, May 27 2018
STATUS
approved