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A259398
Numbers n such that numerator(sigma(n)/n) = reverse(denominator(sigma(n)/n)).
1
1, 69, 879, 1456, 67984, 100464, 185562, 899979, 1936935, 3043383, 5205564, 6638505, 14166720, 15332352, 24111360, 31231431, 59750964, 212464896, 354078153, 445368330, 1058445648, 2317488316, 2761626465, 2869182400, 3097104192, 3296170752, 4179222528, 4675532364
OFFSET
1,2
LINKS
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