A372013 G.f. A(x) satisfies A(x) = 1/( 1 + x*(1 - 9*x*A(x))^(1/3) ).
1, -1, 4, -1, 46, 149, 1351, 8441, 63499, 462752, 3514807, 26923478, 209566927, 1647633779, 13079663527, 104649229988, 843120766711, 6833665175513, 55683581174641, 455878084448132, 3748025535972448, 30931714278955736, 256150668109462507
Offset: 0
Keywords
Programs
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PARI
a(n) = (-1)^n*sum(k=0, n, 9^(n-k)*binomial(n, k)*binomial(k/3, n-k)/(n-k+1));
Formula
a(n) = (-1)^n * Sum_{k=0..n} 9^(n-k) * binomial(n,k) * binomial(k/3,n-k)/(n-k+1).