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A356456
Numbers k not divisible by 3 such that 2*k^2 is not in A014567.
2
10, 28, 40, 50, 70, 77, 110, 130, 133, 136, 140, 154, 155, 160, 161, 170, 176, 190, 196, 200, 209, 224, 230, 250, 259, 266, 275, 280, 290, 308, 310, 322, 350, 364, 370, 371, 377, 385, 410, 416, 418, 430, 440, 469, 470, 476, 490, 496, 518, 520, 530, 532, 539, 550, 553, 590
OFFSET
1,1
COMMENTS
Numbers k not divisible by 3 such that k and sigma(2*k^2) are not coprime, sigma = A000203.
Note that if m is twice a square, then sigma(m) is divisible by 3 (cf. A065766).
LINKS
Jianing Song, Table of n, a(n) for n = 1..11669 (all terms <= 100000)
EXAMPLE
28 is a term since 28 and sigma(2*28^2) = 3591 have a common factor 7, and 28 is not divisible by 3.
PROG
(PARI) isA356456(n) = (n%3) && gcd(n, sigma(2*n^2))>1
CROSSREFS
Equals A356453 \ A008585.
Sequence in context: A022422 A113962 A031105 * A302529 A054501 A112353
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Aug 07 2022
STATUS
approved