A364621 G.f. satisfies A(x) = 1/(1-x)^2 + x*A(x)^4.
1, 3, 15, 118, 1125, 11805, 131431, 1524090, 18208749, 222570985, 2770129627, 34985756752, 447243818573, 5775955923428, 75245253495035, 987627627396792, 13048147674230169, 173382031819242855, 2315662483861709467, 31068798980975635130, 418552735866147739185
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(n+5*k+1, 6*k+1)*binomial(4*k, k)/(3*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(n+5*k+1,6*k+1) * binomial(4*k,k) / (3*k+1).