A344787 a(n) = n * Sum_{d|n} sigma_d(d) / d, where sigma_k(n) is the sum of the k-th powers of the divisors of n.

1, 7, 31, 287, 3131, 47527, 823551, 16843583, 387440266, 10009772937, 285311670623, 8918294639219, 302875106592267, 11112685050294387, 437893920912795941, 18447025553014982271, 827240261886336764195, 39346558271492953948522, 1978419655660313589123999

Offset

1,2

Comments

If p is prime, a(p) = p * Sum_{d|p} sigma_d(d) / d = p * (1 + (1^p + p^p)/p) = 1 + p + p^p.

Links

Seiichi Manyama, Table of n, a(n) for n = 1..386

Formula

G.f.: Sum_{k>=1} sigma_k(k) * x^k/(1 - x^k)^2. - Seiichi Manyama, Dec 16 2022

Example

a(4) = 4 * Sum_{d|4} sigma_d(d) / d = 4 * ((1^1)/1 + (1^2 + 2^2)/2 + (1^4 + 2^4 + 4^4)/4) = 287.

Mathematica

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

Prog

(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, sigma(k, k)*x^k/(1-x^k)^2)) \\ Seiichi Manyama, Dec 16 2022

Crossrefs

Cf. A245466, A321141, A334874, A343781, A344434, A344480.

Cf. A001001, A007429, A027847, A027848, A060640.

Sequence in context: A221875 A143564 A352411 * A253596 A298958 A153028

Adjacent sequences: A344784 A344785 A344786 * A344788 A344789 A344790

Keyword

nonn

Author

Wesley Ivan Hurt, May 28 2021

Status

approved