A371681 G.f. satisfies A(x) = ( 1 + x * A(x) * (1 + A(x)) )^3.
1, 6, 66, 926, 14706, 251622, 4524786, 84310014, 1613384994, 31521329670, 626151135330, 12608193099294, 256769542135314, 5279533270393446, 109449833201392530, 2285215031994672894, 48011502768234360642, 1014265693597636966662
Offset: 0
Keywords
Programs
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PARI
a(n, r=3, t=3, u=3) = r*sum(k=0, n, binomial(n, k)*binomial(t*n+u*k+r, n)/(t*n+u*k+r));
Formula
G.f.: B(x)^3 where B(x) is the g.f. of A364167.
a(n) = Sum_{k=0..n} binomial(n,k) * binomial(3*n+3*k+3,n)/(n+k+1).