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A356449
Numbers k such that 2*k^2 is in A014567.
5
1, 2, 4, 5, 7, 8, 11, 13, 14, 16, 17, 19, 20, 22, 23, 25, 26, 29, 31, 32, 34, 35, 37, 38, 41, 43, 44, 46, 47, 49, 52, 53, 55, 56, 58, 59, 61, 62, 64, 65, 67, 68, 71, 73, 74, 76, 79, 80, 82, 83, 85, 86, 88, 89, 91, 92, 94, 95, 97, 98, 100, 101, 103, 104, 106, 107, 109, 112, 113
OFFSET
1,2
COMMENTS
Numbers k such that k and sigma(2*k^2) are coprime, sigma = A000203.
No term can be a multiple of 3 since 3 divides sigma(m) if m is twice a square (cf. A065766).
LINKS
Jianing Song, Table of n, a(n) for n = 1..11086 (all terms <= 20000)
EXAMPLE
20 is a term since 20 and sigma(2*20^2) = 1953 are coprime.
PROG
(PARI) isA356449(n) = gcd(n, sigma(2*n^2))==1
CROSSREFS
Sequence in context: A368364 A290334 A206285 * A229303 A262978 A112886
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Aug 07 2022
STATUS
approved