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A259398
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Numbers n such that numerator(sigma(n)/n) = reverse(denominator(sigma(n)/n)).
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1
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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
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OFFSET
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1,2
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LINKS
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Antoine Mathys, Table of n, a(n) for n = 1..35
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EXAMPLE
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For n=1, sigma(1)/1 = 1/1.
For n=69, sigma(69)/69 = 32/23.
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MATHEMATICA
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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 *)
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PROG
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(PARI) isok(n) = my(ab= sigma(n)/n); digits(numerator(ab)) == Vecrev(digits(denominator(ab)));
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CROSSREFS
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Cf. A004086, A017665, A017666.
Sequence in context: A264288 A360359 A113707 * A093269 A108147 A160788
Adjacent sequences: A259395 A259396 A259397 * A259399 A259400 A259401
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KEYWORD
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nonn,base,hard
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AUTHOR
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Michel Marcus, Jun 26 2015
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EXTENSIONS
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a(21) from Ivan N. Ianakiev, Jun 30 2015
a(22)-a(28) from Antoine Mathys, Jul 01 2015
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STATUS
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approved
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