OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)
FORMULA
mu(sigma_2(a(n))) = 0.
MATHEMATICA
Do[s=MoebiusMu[DivisorSigma[2, n]]; If[Equal[s, 0], Print[n]], {n, 1, 1000}]
Select[Range[130], !SquareFreeQ[DivisorSigma[2, #]]&] (* Harvey P. Dale, Oct 10 2011 *)
PROG
(PARI) is(k) = !issquarefree(sigma(k, 2)); \\ Amiram Eldar, Aug 12 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Mar 19 2003
STATUS
approved