A366216 G.f. A(x) satisfies A(x) = 1 + x*(1 + x)^4*A(x)^4.
1, 1, 8, 60, 520, 4886, 48384, 497460, 5259872, 56834345, 624819148, 6966612604, 78592083420, 895432704860, 10288759392156, 119089472755860, 1387274092156508, 16251727492295812, 191342076640423136, 2262894045516407118, 26869820052175649836
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(4*k, n-k)*binomial(4*k, k)/(3*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(4*k,n-k) * binomial(4*k,k)/(3*k+1).