A325637 Numbers k for which gcd(2k, sigma(k)) = 2k.

6, 28, 496, 8128, 30240, 32760, 2178540, 23569920, 33550336, 45532800, 142990848, 1379454720, 8589869056, 43861478400, 66433720320, 137438691328, 153003540480, 403031236608, 704575228896, 181742883469056, 6088728021160320, 14942123276641920, 20158185857531904, 275502900594021408, 622286506811515392, 2305843008139952128

Offset: 1

Author

Antti Karttunen, May 21 2019

Keywords

• nonn

Comments

Multiply-perfect numbers (A007691) k with an even abundancy index sigma(k)/k. - Amiram Eldar, Jun 26 2024

Links

• Antti Karttunen, Table of n, a(n) for n = 1..1013 (computed from the b-file of A007691 prepared by T. D. Noe, using Flammenkamp's data)
• Index entries for sequences related to sigma(n).
• Index entries for sequences where any odd perfect numbers must occur.

Crossrefs

Cf. A000203, A033879, A224832, A325636, A325638, A325654.

Subsequences: A000396, A336702 (after its initial 1).

Subsequence of A007691.

Programs

PARI

isA325637(n) = ((n+n)==gcd(n+n,sigma(n)));

Formula

a(n) = A224832(n)/2. - Amiram Eldar, Jun 26 2024