A373682 Expansion of e.g.f. exp(x / (1 - x^2)^3) / (1 - x^2).
1, 1, 3, 25, 109, 1401, 11191, 147673, 1887705, 26419249, 454408651, 7265533881, 148341346693, 2804459457385, 63733061703039, 1419987630142201, 35144931608633521, 902380834051682913, 24277141650582775315, 699721521711883149529, 20520810981571082937501
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n\2, binomial(3*n-5*k, k)/(n-2*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/2)} binomial(3*n-5*k,k)/(n-2*k)!.
a(n) == 1 (mod 2).