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A324899
Odd numbers k for which sigma(k) == 3 (mod 4).
6
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
1,1
COMMENTS
These are all squares. Square roots are in A324909.
FORMULA
a(n) = A324909(n)^2. - Amiram Eldar, Apr 05 2024
MATHEMATICA
Select[Range[1, 235, 2]^2, Mod[DivisorSigma[1, #], 4] == 3 &] (* Amiram Eldar, Apr 05 2024 *)
PROG
(PARI) isA324899(n) = ((n%2)&&3==(sigma(n)%4));
CROSSREFS
Intersection of A016754 and A072462.
Cf. A000203, A324909 (square roots).
Cf. A325311 (a subsequence).
Sequence in context: A125335 A126493 A255419 * A338892 A360280 A198436
KEYWORD
nonn
AUTHOR
Antti Karttunen, Apr 20 2019
STATUS
approved