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, 2361183241263023915008, 865268370658615254581248

Offset

1,2

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

Links

Table of n, a(n) for n=1..21.

Prog

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

Crossrefs

Contains subsequence A088832.

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

Sequence in context: A137344 A029524 A357726 * A262539 A101537 A070353

Adjacent sequences: A045766 A045767 A045768 * A045770 A045771 A045772

Keyword

nonn,more

Author

Dan Hoey

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

a(20) from Max Alekseyev, Oct 14 2025

a(21) from Max Alekseyev, Jan 27 2026

Status

approved