OFFSET
1,2
LINKS
Bryan Clair, The Ihara zeta function of the infinite grid, Electron. J. Combin., 21(2) (2014), #P2.16.
FORMULA
a(n) = Sum_{k=0..n} n*(-3)^(n-k)*(n+k)^(-1)*binomial(n+k, 2*k)*binomial(2*k, k)^2). - Michel Marcus, Nov 23 2018
MAPLE
f:=n->add( n*(-3)^(n-k)*(n+k)^(-1)*binomial(n+k, 2*k)*binomial(2*k, k)^2, k=0..n);
[seq(f(n), n=1..30)];
PROG
(PARI) a(n) = sum(k=0, n, n*(-3)^(n-k)*(n+k)^(-1)*binomial(n+k, 2*k)*binomial(2*k, k)^2); \\ Michel Marcus, Nov 23 2018
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, May 12 2014
STATUS
approved