A324899 Odd numbers k for which sigma(k) == 3 (mod 4).

25, 169, 225, 289, 841, 1225, 1369, 1521, 1681, 2025, 2601, 2809, 3025, 3721, 5329, 7569, 7921, 8281, 9025, 9409, 10201, 11025, 11881, 12321, 12769, 13225, 13689, 14161, 15129, 15625, 18225, 18769, 20449, 22201, 23409, 24025, 24649, 25281, 27225, 29929, 32761, 33489, 34969, 37249, 38809, 41209, 46225, 47961, 52441, 54289, 55225

Offset: 1

Author

Antti Karttunen, Apr 20 2019

Keywords

• nonn

Comments

These are all squares. Square roots are in A324909.

Links

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

Crossrefs

Intersection of A016754 and A072462.

Cf. A000203, A324909 (square roots).

Cf. A325311 (a subsequence).

Programs

Mathematica

Select[Range[1, 235, 2]^2, Mod[DivisorSigma[1, #], 4] == 3 &] (* Amiram Eldar, Apr 05 2024 *)

PARI

isA324899(n) = ((n%2)&&3==(sigma(n)%4));

Formula

a(n) = A324909(n)^2. - Amiram Eldar, Apr 05 2024