A350503 Self-convolution of sigma_n(n).

1, 10, 81, 826, 9766, 141448, 2371173, 46285454, 1025108476, 25583455958, 709014239914, 21645251877538, 721074846998772, 26036416881319860, 1012400617533469985, 42173042024213765280, 1873237518724869171647, 88367918629612594749582, 4411615292876287372479856

Offset: 1

Author

Wesley Ivan Hurt, Jan 06 2022

Keywords

• nonn

Crossrefs

Cf. A023887 (sigma_n(n)).

Programs

Mathematica

Table[Sum[DivisorSigma[k, k]*DivisorSigma[n - k + 1, (n - k + 1)], {k, n}], {n, 20}]

Formula

a(n) = Sum_{k=1..n} A023887(k) * A023887(n-k+1).

a(n) ~ 2*n^n. - Vaclav Kotesovec, Aug 20 2025