A366183 G.f. A(x) satisfies A(x) = 1/(1 - x)^3 + x*A(x)^3/(1 - x)^2.
1, 4, 20, 145, 1250, 11746, 116641, 1204039, 12790067, 138895021, 1535005454, 17207743738, 195197256289, 2236419124408, 25842382083071, 300822398531482, 3524358836945936, 41524956284752018, 491722951928324392, 5848997420625891294, 69854562522309219081
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(n+7*k+2, n-k)*binomial(3*k, k)/(2*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(n+7*k+2,n-k) * binomial(3*k,k)/(2*k+1).