OFFSET
1,2
LINKS
Antoine Mathys, Table of n, a(n) for n = 1..35
EXAMPLE
For n=1, sigma(1)/1 = 1/1.
For n=69, sigma(69)/69 = 32/23.
MATHEMATICA
fQ[n_]:=Numerator[DivisorSigma[1, n]/n]==FromDigits[Reverse[ IntegerDigits[Denominator[DivisorSigma[1, n]/n]]]];
Select[Range[10^6], fQ[#]&] (* Ivan N. Ianakiev, Jun 30 2015 *)
PROG
(PARI) isok(n) = my(ab= sigma(n)/n); digits(numerator(ab)) == Vecrev(digits(denominator(ab)));
CROSSREFS
KEYWORD
nonn,base,hard
AUTHOR
Michel Marcus, Jun 26 2015
EXTENSIONS
a(21) from Ivan N. Ianakiev, Jun 30 2015
a(22)-a(28) from Antoine Mathys, Jul 01 2015
STATUS
approved