A373685 Expansion of e.g.f. exp(x / (1 - x^3)^2) / (1 - x^3).
1, 1, 1, 7, 73, 301, 1561, 32131, 306097, 2062873, 43102801, 720515071, 7245589561, 136364378437, 3259345980073, 47903339552251, 873735377165281, 25383884535029041, 515592396859327777, 10003196649764818423, 316630570292623967401, 8359224513085985870941
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n\3, binomial(2*n-5*k, k)/(n-3*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/3)} binomial(2*n-5*k,k)/(n-3*k)!.
a(n) == 1 (mod 6).