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URL: https://oeis.org/A146747

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A146747
Numbers k such that sigma_1(k)*sigma_0(k)/(sigma_1(k)-sigma_0(k)) is an integer.
1
2, 3, 5, 6, 7, 20, 30
OFFSET
1,1
COMMENTS
Numbers k such that A000203(k)*A000005(k)/(A000203(k)-A000005(k)) is an integer.
MATHEMATICA
q[n_] := Module[{s = DivisorSigma[1, n], d = DivisorSigma[0, n]}, Divisible[s*d, s - d]]; Select[Range[2, 100], q] (* Amiram Eldar, Apr 07 2024 *)
PROG
(PARI) is(n) = {my(f = factor(n), s = sigma(f), d = numdiv(f)); n > 1 && !((s*d) % (s-d)); } \\ Amiram Eldar, Apr 07 2024
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Ctibor O. Zizka, Nov 01 2008
STATUS
approved