OFFSET
1,2
COMMENTS
Also numbers k that divide A060640(k). - Seiichi Manyama, May 08 2021
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..100 (terms 1..64 from Michel Marcus)
MATHEMATICA
f[p_, e_] := ((e + 1)*p^(e + 2) - (e + 2)*p^(e + 1) + 1)/(p - 1)^2; q[1] = True; q[n_] := Divisible[Times @@ f @@@ FactorInteger[n], n]; Select[Range[10^6], q] (* Amiram Eldar, Dec 29 2024 *)
PROG
(PARI) for(n=1, 10^7, if(frac(sumdiv(n, d, sigma(d)/d))==0, print1(n, ", ")))
(PARI) is(k) = {my(f = factor(k)); !(prod(i = 1, #f~, p = f[i, 1]; e = f[i, 2]; ((e + 1)*p^(e + 2) - (e + 2)*p^(e + 1) + 1)/(p - 1)^2) % k); } \\ Amiram Eldar, Dec 29 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Apr 06 2002
EXTENSIONS
More terms from Jason Earls, Apr 09 2002
a(22)-a(25) from Jinyuan Wang, Apr 06 2020
a(26)-a(32) from Michel Marcus, Apr 06 2020
STATUS
approved