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A354039 Odd numbers k for which sigma(k^2) == 1 (mod 4). 1
1, 3, 7, 9, 11, 19, 21, 23, 25, 27, 31, 33, 43, 47, 49, 57, 59, 63, 65, 67, 69, 71, 75, 77, 79, 81, 83, 85, 93, 99, 103, 107, 121, 127, 129, 131, 133, 139, 141, 145, 147, 151, 161, 163, 167, 169, 171, 175, 177, 179, 185, 189, 191, 195, 199, 201, 205, 207, 209, 211, 213, 217, 221, 223, 225, 227, 231, 237, 239, 243 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
MATHEMATICA
Select[2*Range[120] - 1, Divisible[DivisorSigma[1, #^2] - 1, 4] &] (* Amiram Eldar, May 16 2022 *)
PROG
(PARI)
A354036(n) = ((n%2)&&1==(sigma(n*n)%4));
isA354039(n) = A354036(n);
CROSSREFS
Cf. A000035, A000203, A010873, A065764, A083025, A354036 (characteristic function).
Cf. also A324909.
Sequence in context: A088630 A129747 A354570 * A004614 A112398 A197504
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 16 2022
STATUS
approved

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Last modified March 28 21:54 EDT 2024. Contains 371254 sequences. (Running on oeis4.)