A356382 Even terms in A014567.

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

Author

Jianing Song, Aug 07 2022

Keywords

• nonn
• easy

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).

Examples

			3362 is a term since 3362 and sigma(3362) = 5169 are coprime.
3364 is a term since 3364 and sigma(3364) = 6097 are coprime.
		

Links

• Jianing Song, Table of n, a(n) for n = 1..7575 (all terms <= 10^8)

Crossrefs

Cf. A014567, A000203, A065766.

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}.

Programs

PARI

isA356382(n) = !(n%2) && gcd(n, sigma(n))==1