login
A356382
Even terms in A014567.
4
2, 4, 8, 16, 32, 36, 50, 64, 98, 100, 128, 144, 242, 256, 324, 338, 392, 400, 484, 512, 576, 578, 676, 722, 784, 800, 900, 968, 1024, 1058, 1156, 1250, 1296, 1352, 1444, 1600, 1682, 1922, 1936, 2048, 2116, 2304, 2312, 2450, 2500, 2704, 2738, 2888, 2916, 3136, 3362, 3364
OFFSET
1,1
COMMENTS
Even numbers k such that k and sigma(k) are coprime, sigma = A000203.
Each term is an even square or twice a square.
No term can be of the form 18*k^2 since sigma(m) is divisible by 3 if m is twice a square (cf. A065766).
LINKS
Jianing Song, Table of n, a(n) for n = 1..7575 (all terms <= 10^8)
EXAMPLE
3362 is a term since 3362 and sigma(3362) = 5169 are coprime.
3364 is a term since 3364 and sigma(3364) = 6097 are coprime.
PROG
(PARI) isA356382(n) = !(n%2) && gcd(n, sigma(n))==1
CROSSREFS
Subsequence of A088827. Includes A000079 as a subsequence.
Equals {A356448(n)^2} U {2*A356449(n)^2} = {2*A356449(n)^2} U {4*A356451(n)^2}.
Sequence in context: A072011 A068535 A272034 * A051505 A353720 A371294
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Aug 07 2022
STATUS
approved