A324909 Odd numbers k for which sigma(k^2) == 3 (mod 4).

5, 13, 15, 17, 29, 35, 37, 39, 41, 45, 51, 53, 55, 61, 73, 87, 89, 91, 95, 97, 101, 105, 109, 111, 113, 115, 117, 119, 123, 125, 135, 137, 143, 149, 153, 155, 157, 159, 165, 173, 181, 183, 187, 193, 197, 203, 215, 219, 229, 233, 235, 241, 245, 247, 257, 259, 261, 267, 269, 273, 277, 281, 285, 287, 291, 293, 295, 299, 303, 313

Offset

1,1

Comments

Odd numbers with an odd number of prime factors congruent to 1 modulo 4, or odd members of A209922. - Charlie Neder, Apr 24 2019

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Index entries for sequences related to sigma(n).

Formula

a(n) = sqrt(A324899(n)).

Mathematica

Select[Range[1, 315, 2], Mod[DivisorSigma[1, #^2], 4] == 3 &] (* Amiram Eldar, Apr 05 2024 *)

Prog

(PARI) isA324909(n) = ((n%2)&&3==(sigma(n*n)%4));

Crossrefs

Cf. A000203, A000196, A324899.

Cf. A325312 (a subsequence).

Cf. A209922 (a supersequence).

Sequence in context: A090758 A327922 A309812 * A322105 A230503 A335695

Adjacent sequences: A324906 A324907 A324908 * A324910 A324911 A324912

Keyword

nonn

Author

Antti Karttunen, Apr 20 2019

Status

approved