A384258 - OEIS

A384258

a(n) = Product_{k=0..n-1} (n+4*k+1).

1, 2, 21, 384, 9945, 332640, 13627845, 660602880, 36974963025, 2346549004800, 166490632833525, 13059009124761600, 1122040194333683625, 104802322548059136000, 10572978481108199281125, 1145749403453003661312000, 132730561036298082383150625, 16369108295524571830763520000

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..17.

FORMULA

a(n) = 4^n * RisingFactorial((n+1)/4,n).

a(n) = n! * [x^n] 1/(1 - 4*x)^((n+1)/4).

PROG

(PARI) a(n) = prod(k=0, n-1, n+4*k+1);

(SageMath)

def a(n): return 4^n*rising_factorial((n+1)/4, n)