A045769 Numbers k such that sigma(k) == 4 (mod k).

1, 3, 9, 12, 70, 88, 1888, 4030, 5830, 32128, 521728, 1848964, 8378368, 34359083008, 66072609790, 549753192448, 259708613909470, 2251799645913088, 9223372026117357568

Offset: 1

Author

Dan Hoey

Keywords

• nonn
• more

Comments

Every number of the form 2^(j-1)*(2^j - 5), where 2^j - 5 is prime, is a term. See A059608. - Jon E. Schoenfield, Jun 02 2019

Crossrefs

Contains subsequence A088832.

Cf. A054024, A045768, A059608, A088834, A045770, A076496.

Programs

PARI

isok(k) = Mod(sigma(k), k) == 4; \\ Michel Marcus, Jan 04 2023

Extensions

a(13) from Harvey P. Dale, Mar 20 2011

Initial term 1 inserted and a(14)-a(16) from Donovan Johnson, Mar 01 2012

Term 3 inserted by Michel Marcus, Jan 04 2023

a(18) from Jon E. Schoenfield confirmed, and a(17), a(19) added by Max Alekseyev, Jun 08 2025