A373521 Expansion of e.g.f. exp(x/(1 - x^4)^(3/4)).
1, 1, 1, 1, 1, 91, 541, 1891, 5041, 249481, 3424681, 24365881, 119821681, 4208219731, 96849813061, 1133147785771, 8728726799521, 251218306095121, 8116398738418321, 138787857114672241, 1523943014238675361, 39648007379230971211, 1599866285860593980461
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n\4, binomial(3*n/4-2*k-1, k)/(n-4*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/4)} binomial(3*n/4-2*k-1,k)/(n-4*k)!.
a(n) == 1 mod 90.