OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000, corrected by Sidney Cadot, Feb 05 2023
EXAMPLE
6*p is a solution if p > 3 is prime, since sigma(6*p) = 1 + 2 + 3 + 6 + p + 2*p + 3*p + 6*p = 12*(p+1) = 2*6*p + 12 = 2*k + 12. These are "regular" solutions. Also k = 121, 304 are "singular" solutions. See other remainders in cross-references.
MATHEMATICA
Select[Range[2000], Mod[DivisorSigma[1, #] - 12, #] == 0 &] (* Vincenzo Librandi, Mar 11 2014, corrected by Amiram Eldar, Jan 04 2023 *)
PROG
(PARI) isok(k) = Mod(sigma(k), k) == 12; \\ Michel Marcus, Jan 04 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Oct 21 2002
EXTENSIONS
Initial term 1 added by Vincenzo Librandi, Mar 11 2014
Terms 6 and 11 inserted by Michel Marcus, Jan 04 2023
STATUS
approved