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
PROG
(PARI) isok(k) = Mod(sigma(k), k) == 4; \\ Michel Marcus, Jan 04 2023
CROSSREFS
KEYWORD
nonn,more
AUTHOR
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