A373681 Expansion of e.g.f. exp(x / (1 - x^2)^2) / (1 - x^2).
1, 1, 3, 19, 85, 861, 6391, 74383, 822249, 10724185, 156044971, 2331428331, 40840033213, 706624333429, 14138302767135, 281981427966631, 6273491346471121, 142296558637593393, 3475950835899954259, 88235303457193306435, 2351639524607386287141
Offset: 0
Keywords
Programs
-
PARI
a(n) = n!*sum(k=0, n\2, binomial(2*n-3*k, k)/(n-2*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/2)} binomial(2*n-3*k,k)/(n-2*k)!.
a(n) == 1 (mod 2).