A325312 Odd numbers k for which sigma(k^2) == 3 (mod 4) and sigma(k^2) > 2*k^2.

105, 315, 495, 735, 945, 1155, 1485, 1995, 2205, 2415, 2625, 2835, 2925, 3135, 3255, 3315, 3465, 3795, 4455, 4515, 4935, 5115, 5145, 5445, 5655, 5985, 6195, 6615, 6825, 7035, 7095, 7245, 7455, 7605, 7755, 7875, 8085, 8295, 8505, 8715, 8775, 8925, 9009, 9405, 9735, 9765, 9945, 10395, 10725, 10815, 11235, 11385, 11781, 12375

Offset: 1

Author

Antti Karttunen, Apr 20 2019

Keywords

• nonn

Comments

Square roots of A325311, odd abundant numbers k for which sigma(k) == 3 mod 4.

Links

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

Crossrefs

Cf. A000196, A325311.

Intersection of A174830 and A324909.

Programs

Mathematica

Select[Range[1, 12375 , 2], Mod[(s = DivisorSigma[1, #^2]), 4] == 3 && s > 2*#^2 &] (* Amiram Eldar, Apr 05 2024 *)

PARI

isA325312(n) = { my(t=sigma(n*n)); (n%2 && 3==(t%4) && t>(2*n*n)); };

Formula

a(n) = sqrt(A325311(n)).