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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 (list; graph; refs; listen; history; text; internal format)
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

Cf. A004086, A017665, A017666.

Sequence in context: A211692 A264288 A113707 * A093269 A108147 A160788

Adjacent sequences:  A259395 A259396 A259397 * A259399 A259400 A259401

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

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Last modified August 16 10:49 EDT 2022. Contains 356168 sequences. (Running on oeis4.)