A378787 G.f. A(x) satisfies A(x) = ( 1 + x * (1 + x*A(x)^2)^3 )^2.
1, 2, 7, 36, 197, 1184, 7425, 48308, 322521, 2198064, 15227850, 106924154, 759245463, 5442675080, 39335090088, 286296369000, 2096706604597, 15439417451928, 114243931954962, 849030345258990, 6334510149389409, 47428709540589036, 356261301882333885
Offset: 0
Keywords
Programs
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PARI
a(n, r=2, s=3, t=0, u=4) = r*sum(k=0, n, binomial(t*k+u*(n-k)+r, k)*binomial(s*k, n-k)/(t*k+u*(n-k)+r));
Formula
a(n) = Sum_{k=0..n} binomial(4*(n-k)+2,k) * binomial(3*k,n-k)/(2*(n-k)+1).
G.f.: A(x) = B(x)^2 where B(x) is the g.f. of A137957.