A371798 - OEIS

A371798

a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(2*n-2*k-1,n-2*k).

1, 1, 2, 7, 26, 96, 356, 1331, 5014, 19006, 72412, 277058, 1063856, 4097510, 15823432, 61245987, 237536326, 922906150, 3591500972, 13996328322, 54614894396, 213360770840, 834409399672, 3266370155262, 12797894251276, 50184309630196, 196936674150296

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..26.

FORMULA

a(n) = [x^n] 1/((1+x^2) * (1-x)^n).

a(n) = binomial(2*n-1, n)*hypergeom([1, (1-n)/2, -n/2], [1/2-n, 1-n], -1). - Stefano Spezia, Apr 06 2024

a(n) ~ 2^(2*n+1) / (5*sqrt(Pi*n)). - Vaclav Kotesovec, Apr 07 2024

PROG

(PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(2*n-2*k-1, n-2*k));

CROSSREFS

Cf. A026641, A120305.

Sequence in context: A188860 A129273 A055988 * A275013 A278351 A001075

Adjacent sequences: A371795 A371796 A371797 * A371799 A371800 A371801

KEYWORD

nonn

AUTHOR

Seiichi Manyama, Apr 06 2024

STATUS

approved