A343781 a(n) = Sum_{k=1..floor(n/2)} sigma_k(n-k), where sigma_k(n) is the sum of the k-th powers of the divisors of n.

0, 1, 3, 9, 17, 55, 111, 457, 943, 4962, 11148, 69526, 159402, 1161340, 2765874, 22829766, 55192956, 510771772, 1257880780, 12870681814, 32042113008, 359566186586, 904795505226, 11043196798176, 28002785395660, 369463867367567, 943392140873807, 13378621275148931

Offset

1,3

Links

Table of n, a(n) for n=1..28.

Example

a(5) = 17; a(5) = Sum_{i=1..2} sigma_k(5-k) = sigma_1(4) + sigma_2(3) = (1+2+4) + (1^2+3^2) = 7 + 10 = 17.

Mathematica

Table[Sum[DivisorSigma[i, n - i], {i, Floor[n/2]}], {n, 30}]

Prog

(PARI) a(n) = sum(k=1, n\2, sigma(n-k, k)); \\ Michel Marcus, Apr 29 2021

Crossrefs

Cf. A245466.

Sequence in context: A173140 A018307 A108050 * A321869 A009211 A105538

Adjacent sequences: A343778 A343779 A343780 * A343782 A343783 A343784

Keyword

nonn

Author

Wesley Ivan Hurt, Apr 29 2021

Status

approved