OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
46 = 2*23 and sigma(46)/phi(46) = 72/22 is not an integer, so 46 is in the sequence.
MATHEMATICA
Do[s=DivisorSigma[1, n]/EulerPhi[n]; If[ !IntegerQ[s]&&!PrimeQ[n], Print[n]], {n, 1, 256}]
Select[Range[150], CompositeQ[#]&&!IntegerQ[DivisorSigma[1, #]/ EulerPhi[ #]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 19 2020 *)
PROG
(PARI) lista(nn) = forcomposite(n=1, nn, if (denominator(sigma(n)/eulerphi(n)) != 1, print1(n, ", "))); \\ Michel Marcus, Jul 11 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 04 2002
STATUS
approved