A356341 a(n) = Sum_{k=1..n} binomial(2*n, k) * sigma(k).

2, 22, 131, 806, 3607, 20395, 84254, 422230, 1842359, 8616007, 33843614, 173724659, 676938316, 2983855666, 12806013721, 57981927158, 223432922515, 1040923729567, 4004885305320, 18277809794671, 75668287229078, 317458937099194, 1215454524390767, 5785782106653667

Offset: 1

Author

Vaclav Kotesovec, Aug 04 2022

Keywords

• nonn

Crossrefs

Cf. A000203, A024916, A185003, A351146.

Programs

Mathematica

Table[Sum[Binomial[2*n, k]*DivisorSigma[1, k], {k, 1, n}], {n, 1, 30}]

PARI

a(n) = sum(k=1, n, binomial(2*n, k) * sigma(k)); \\ Michel Marcus, Aug 05 2022

Formula

a(n) ~ Pi^2 * n * 4^(n-1) / 3.