A086894 a(n) = (A000522(2*n) + 1)/2.

1, 3, 33, 979, 54801, 4932051, 651030673, 118487582403, 28437019776609, 8701728051642211, 3306656659624040001, 1527675376746306480243, 843276807963961177093873, 548129925176574765111017139, 414386223433490522423928956721, 360516014387136754508818192346851

Offset: 0

Author

Vladeta Jovovic, Aug 22 2003

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..100

Crossrefs

Cf. A000522.

Programs

PARI

a(n)={(1 + sum(k=0, 2*n, (2*n)!/k!))/2} \\ Andrew Howroyd, Jan 05 2020

Formula

a(n) = (1 + (2*n)!*Sum_{k=0..2*n} 1/k!)/2. - Andrew Howroyd, Jan 05 2020

Extensions

Terms a(11) and beyond from Andrew Howroyd, Jan 05 2020