A067680 Numbers k such that sigma(2k + 2) = 4k.

6, 21, 54, 75, 441, 1071, 4191, 9315, 58311, 4197375, 7685151, 36997695, 268460031, 1073790975, 17180065791, 13517087570210304, 18014398710808575, 288230376957018111

Offset: 1

Author

Benoit Cloitre, Feb 04 2002

Keywords

• nonn
• more

Comments

If k is a term, then 2*k + 2 is a term of A125246. - Jinyuan Wang, Apr 08 2020

Crossrefs

Cf. A000203, A125246.

Programs

PARI

isok(k) = sigma(2*k+2) == 4*k; \\ Michel Marcus, Apr 06 2020

Extensions

a(9) from Benoit Cloitre and Neven Juric (neven.juric(AT)apis-it.hr), May 21 2004

a(10)-a(15) from Donovan Johnson, Jan 31 2009

a(16)-a(18) from Jinyuan Wang, Apr 06 2020