A274774 - OEIS

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A274774

Least k such that sigma(k*n)/tau(k*n) = sigma(k*n+1)/tau(k*n+1), or 0 if no such k exists.

5, 7, 895, 1363, 1, 3353, 2, 2589, 1007, 10341, 1265, 1726, 7, 1, 179, 6634, 10052, 5745, 86, 53389, 958, 12165, 58, 863, 649, 250017, 2395, 6103, 46, 3447, 2714, 3317, 8110, 5026, 22653, 2812637, 94, 43, 16795, 58069, 61693, 479, 38, 52790, 1437, 29, 74, 2027510, 122367, 70545

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OFFSET

1,1

COMMENTS

Corresponding averages are 3, 6, 540, 840, 3, 2880, 6, 3240, 1170, 8640, 1596, 3240, 28, 6, 540, 9072, 15120, 8640, 330, 55440, 2880, 21924, 270, 3240, 1860, 875070, 7200, ...

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

a(13) = 7 because sigma(7*13)/tau(7*13) = sigma(7*13+1)/tau(7*13+1).

MATHEMATICA

a[n_] := Block[{k=1}, While[! Equal @@ (DivisorSigma[1, n*k + {0, 1}] / DivisorSigma[ 0, n*k + {0, 1}]), k++]; k]; Array[a, 20] (* Giovanni Resta, Jul 28 2016 *)

PROG

(PARI) a(n) = {my(k=1); while (sigma(k*n)/numdiv(k*n) != sigma(k*n+1)/numdiv(k*n+1), k++); k; }

CROSSREFS

Cf. A238380.

Sequence in context: A083687 A101829 A056252 * A370190 A176599 A309409

Adjacent sequences: A274771 A274772 A274773 * A274775 A274776 A274777

KEYWORD

nonn

AUTHOR

Altug Alkan, Jul 28 2016

STATUS

approved