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A356454
Numbers k such that 4*k^2 is not in A014567; complement of A356451.
4
7, 21, 35, 39, 42, 49, 56, 57, 62, 63, 77, 78, 84, 91, 93, 99, 105, 111, 114, 117, 119, 126, 129, 133, 147, 154, 155, 156, 161, 168, 171, 175, 183, 186, 189, 195, 198, 201, 203, 209, 210, 217, 219, 222, 228, 231, 234, 237, 245, 252, 258, 259, 266, 273, 275, 279, 280, 285
OFFSET
1,1
COMMENTS
Numbers k such that k and sigma(4*k^2) are not coprime, sigma = A000203.
LINKS
Jianing Song, Table of n, a(n) for n = 1..12241 (all terms <= 40000)
FORMULA
a(n) = A356452(n)/2.
EXAMPLE
7 is a term since 7 and sigma(4*7^2) = 399 have a common factor 7.
PROG
(PARI) isA356454(n) = gcd(n, sigma(4*n^2))>1
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Aug 07 2022
STATUS
approved