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

1,1

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.

Formula

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

Prog

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

Crossrefs

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

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

Subsequence of A007691.

Sequence in context: A345004 A370789 A351440 * A336702 A325654 A201186

Adjacent sequences: A325634 A325635 A325636 * A325638 A325639 A325640

Keyword

nonn

Author

Antti Karttunen, May 21 2019

Status

approved