OFFSET
1,2
COMMENTS
These numbers appear indirectly in A067740, which seeks the least k such that sigma(k)/sigma(phi(k)) = n. Most of these numbers are even. The odd terms (1, 87, 1257, 41559, 56679, ...) all appear to produce sigma(k)/sigma(phi(k)) = 1.
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[1000], IntegerQ[DivisorSigma[1, #]/DivisorSigma[1, EulerPhi[#]]] &]
PROG
(PARI) is(k) = {my(f = factor(k), s = sigma(f), p = eulerphi(f)); !(s % sigma(p)); } \\ Amiram Eldar, May 17 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, May 11 2011
STATUS
approved