A396599 Odd numbers k where sigma_2(k)/k is an integer.

1, 65, 175, 525, 1105, 5425, 16275, 20737, 30225, 32045, 70525, 86025, 103685, 171275, 200725, 207553, 211575, 352529, 372775, 474075, 513825, 602175, 1037765, 1118325, 1198925, 1264957, 1347905, 1555275, 1762645, 1824877, 2436525, 2609425, 2698189, 3596775

Offset

1,2

Links

Alexander Violette, Table of n, a(n) for n = 1..104

Wikipedia, Divisor function.

Example

65's divisors are 1, 5, 13, and 65. Since (1^2+5^2+13^2+65^2)/65 is an integer, 65 is in this sequence.

Mathematica

Select[Range[1, 4000000, 2], Divisible[DivisorSigma[2, #], #] &] (* Amiram Eldar, Jun 03 2026 *)

Prog

(PARI) isok(k) = (k%2) && (denominator(sigma(k, 2)/k) == 1); \\ Michel Marcus, Jun 03 2026

Crossrefs

Intersection of A005408 and A046762.

Cf. A000203, A001157, A396600, A396601, A396602.

Sequence in context: A044397 A044778 A054902 * A255244 A261989 A051968

Adjacent sequences: A396594 A396597 A396598 * A396600 A396601 A396602

Keyword

nonn

Author

Alexander Violette, May 30 2026

Status

approved