A379192 G.f. A(x) satisfies A(x) = (1 + x*A(x))^3/(1 - x*A(x)^2).
1, 4, 27, 235, 2344, 25374, 289906, 3441015, 42017262, 524418639, 6660297019, 85796763321, 1118314903447, 14722203914653, 195465862293738, 2614323606027841, 35191188308646852, 476390139438508209, 6481416282265645008, 88577523301166187997, 1215421503348039618483
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(n+2*k+1, k)*binomial(3*n+3*k+3, n-k)/(n+2*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(n+2*k+1,k) * binomial(3*n+3*k+3,n-k)/(n+2*k+1).