OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
A. A. Dobrynin, I. Gutman, S. Klavzar, P. Zigert, Wiener Index of Hexagonal Systems , Acta Applicandae Mathematicae 72 (2002), pp. 247-294.
I. Gutman, S. Klavzar, M. Petkovsek, and P. Zigert, On Hosoya polynomials of benzenoid graphs, Comm. Math. Comp. Chem. (MATCH), 43, 2001, 49-66.
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
FORMULA
a(n) = (27 - 26*n + 72*n^2 + 8*n^3)/3.
G.f.: x*(27 + x - 3*x^2 - 9*x^3)/(1-x)^4. - Bruno Berselli, Jul 27 2011
PROG
(Magma) [(27 - 26*n + 72*n^2 +8*n^3)/3: n in [1..30]]; // Vincenzo Librandi, Jul 26 2011
(PARI) a(n)=(8*n^3+72*n^2-26*n)/3+9 \\ Charles R Greathouse IV, Jul 26 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Jul 25 2011
STATUS
approved