A325311 Odd abundant numbers k for which sigma(k) == 3 (mod 4).

11025, 99225, 245025, 540225, 893025, 1334025, 2205225, 3980025, 4862025, 5832225, 6890625, 8037225, 8555625, 9828225, 10595025, 10989225, 12006225, 14402025, 19847025, 20385225, 24354225, 26163225, 26471025, 29648025, 31979025, 35820225, 38378025, 43758225, 46580625, 49491225, 50339025, 52490025, 55577025, 57836025, 60140025

Offset: 1

Author

Antti Karttunen, Apr 20 2019

Keywords

• nonn

Comments

These are all squares. Square roots are in A325312.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to sigma(n).

Crossrefs

Cf. A000203, A324647, A325312 (square roots).

Intersection of A005231 and A324899.

Subsequence of A156942.

Programs

Mathematica

Select[Range[1, 7755, 2]^2, Mod[(s = DivisorSigma[1, #]), 4] == 3 && s > 2*# &] (* Amiram Eldar, Apr 05 2024 *)

PARI

isA325311(n) = (n%2 && (3==sigma(n)%4) && sigma(n)>(2*n));

Formula

a(n) = A325312(n)^2. - Amiram Eldar, Apr 05 2024