A380721 E.g.f. A(x) satisfies A(x) = exp(x / (1 - x*A(x))^3) / (1 - x*A(x))^2.
1, 3, 29, 511, 13313, 462401, 20140495, 1056765711, 64931273601, 4575023966017, 363744086548751, 32219262817769039, 3146690718151835233, 335963164545043929921, 38931639595489583488239, 4866587415704561667715471, 652773358729046023136421377, 93523037570967777721191018881
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Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n, (n-k+1)^(k-1)*binomial(3*n+1, n-k)/k!);
Formula
a(n) = n! * Sum_{k=0..n} (n-k+1)^(k-1) * binomial(3*n+1,n-k)/k!.