A375691 G.f. A(x) satisfies A(x) = 1 + x^4*(1+x)*A(x)^3.
1, 0, 0, 0, 1, 1, 0, 0, 3, 6, 3, 0, 12, 36, 36, 12, 55, 220, 330, 220, 328, 1365, 2730, 2730, 2793, 8841, 21420, 28560, 29172, 62832, 164220, 271320, 314583, 508896, 1265628, 2430480, 3275085, 4642803, 10091664, 21066804, 32555028, 45388200, 85102875
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\4, binomial(k, n-4*k)*binomial(3*k, k)/(2*k+1));
Formula
a(n) = Sum_{k=0..floor(n/4)} binomial(k,n-4*k) * binomial(3*k,k)/(2*k+1).