A372104 G.f. A(x) satisfies A(x) = 1/( 1 - 4*x*A(x)/(1-x) )^(1/2).
1, 2, 12, 86, 686, 5858, 52404, 484814, 4600652, 44534386, 438034928, 4365350062, 43983695242, 447305878226, 4585518132768, 47335424695142, 491615988964766, 5133343692822146, 53858312462193328, 567501135052136702, 6002857276349252630
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, 4^k*binomial(3*k/2-1/2, k)*binomial(n-1, n-k)/(k+1));
Formula
a(n) = Sum_{k=0..n} 4^k * binomial(3*k/2-1/2,k) * binomial(n-1,n-k)/(k+1).