A377889 E.g.f. A(x) satisfies A(x) = exp(x * A(x))/(1 - x*A(x)^3).
1, 2, 21, 472, 16581, 795736, 48509641, 3589729760, 312603962985, 31321633489408, 3549706188092541, 448973808123051520, 62697159481460439469, 9581292408000225087488, 1590488540940006100524657, 284993765391981838318575616, 54826610288277007690469896017
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n, (3*n-2*k+1)^(k-1)*binomial(4*n-3*k, n-k)/k!);
Formula
a(n) = n! * Sum_{k=0..n} (3*n-2*k+1)^(k-1) * binomial(4*n-3*k,n-k)/k!.