OFFSET
1,1
COMMENTS
Cycle graphs defined for n>=3; extended to n=1 using the closed form
LINKS
Eric Weisstein's World of Mathematics, Molecular Topological Index
Index entries for linear recurrences with constant coefficients, signature (2,1,-4,1,2,-1).
FORMULA
a(n) = n*(2*n^2+(-1)^n+15)/4.
a(n) = +2*a(n-1) +1*a(n-2) -4*a(n-3) +1*a(n-4) +2*a(n-5) -1*a(n-6).
G.f.: 4*x*(1+x-x^2+x^3+x^4)/((1-x)^4*(1+x)^2).
PROG
(PARI) a(n)=n*(2*n^2+(-1)^n+15)/4;
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Jul 10 2011
STATUS
approved