A376326 - OEIS

A376326

Expansion of (1/x) * Series_Reversion( x * (1-x-x^2)^4 ).

1, 4, 30, 272, 2737, 29380, 329614, 3818540, 45329440, 548511612, 6740687924, 83898110660, 1055441468145, 13398494365088, 171422870731600, 2208161418665872, 28614197357895055, 372754395074051500, 4878709294080115494, 64123505084010848580, 846018700129069313495

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..20.

Index entries for reversions of series

FORMULA

a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} binomial(4*n+k+3,k) * binomial(5*n-k+3,n-2*k).

G.f.: B(x)^4, where B(x) is the g.f. of A365188.

PROG

(PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x-x^2)^4)/x)

(PARI) a(n, s=2, t=4, u=0) = sum(k=0, n\s, binomial(t*(n+1)+k-1, k)*binomial((t+u+1)*(n+1)-(s-1)*k-2, n-s*k))/(n+1);