OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MAPLE
with(numtheory, sigma):
isA320513 := n -> (n > 1) and issqrfree(n) and (sigma(sigma(sigma(n))) < 3*n+1):
S := select(isA320513, [$1..100000]);
MATHEMATICA
Rest[Select[Range[100000], SquareFreeQ[#] && DivisorSigma[1, DivisorSigma[1, DivisorSigma[1, #]]] < 3*# + 1 &]] (* Vaclav Kotesovec, Oct 14 2018 *)
PROG
(PARI) isok(n) = (n>1) && issquarefree(n) && (sigma(sigma(sigma(n))) < 3*n + 1); \\ Michel Marcus, Oct 14 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Oct 14 2018
STATUS
approved