A371617 G.f. satisfies A(x) = ( 1 + x / (1 - x*A(x)^3)^3 )^2.
1, 2, 7, 54, 419, 3644, 33366, 317672, 3113559, 31200060, 318219653, 3292546660, 34475311605, 364621943538, 3889561661610, 41799988930926, 452126713579192, 4918321519144206, 53773399008883695, 590578523863692086, 6512515698908748358
Offset: 0
Keywords
Links
- Seiichi Manyama, Table of n, a(n) for n = 0..934
Programs
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PARI
a(n, r=2, s=3, t=0, u=6) = r*sum(k=0, n, binomial(t*k+u*(n-k)+r, k)*binomial(n+(s-1)*k-1, n-k)/(t*k+u*(n-k)+r));
Formula
a(n) = Sum_{k=0..n} binomial(6*(n-k)+2,k) * binomial(n+2*k-1,n-k)/(3*(n-k)+1).