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

Offset

1,2

Comments

a(17) > 10^12. - Donovan Johnson, Mar 01 2012

a(17) > 10^13. - Giovanni Resta, Apr 02 2014

a(17) > 1.5*10^14. - Jud McCranie, Jun 02 2019

a(17) <= 2251799645913088. 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..16.

Prog

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

Crossrefs

Cf. A054024, A045768, A045769, A088834, A045770, A076496.

Cf. A059608.

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

Status

approved