OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..n} [x^(2n-2k)] Product_{j=0..[k/2]} 1/(1 - (2j + k-2[k/2])^2*x^2).
PROG
(PARI) {a(n)=sum(k=0, n, polcoeff(1/prod(j=0, k\2, 1-(2*j+(k%2))^2*x^2 +x*O(x^(2*n-2*k))), 2*n-2*k))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jan 14 2008
STATUS
approved