A243473 - OEIS

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A243473

a(n) = numerator(sigma(n)/n) - denominator(sigma(n)/n) where sigma(n) = sum of divisors of n.

6

0, 1, 1, 3, 1, 1, 1, 7, 4, 4, 1, 4, 1, 5, 3, 15, 1, 7, 1, 11, 11, 7, 1, 3, 6, 8, 13, 1, 1, 7, 1, 31, 5, 10, 13, 55, 1, 11, 17, 5, 1, 9, 1, 10, 11, 13, 1, 19, 8, 43, 7, 23, 1, 11, 17, 8, 23, 16, 1, 9, 1, 17, 41, 63, 19, 13, 1, 29, 9, 37, 1, 41, 1, 20, 49, 16

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OFFSET

1,4

COMMENTS

a(n) = 1 for n prime or perfect (A053813).

a(n) = A001065(n) when n is in A014567.

a(n) > n for n in A069057. - Michel Marcus, May 04 2016

LINKS

Michel Marcus, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A017665(n) - A017666(n).

MATHEMATICA

f[n_] := DivisorSigma[1, n]/n; Table[Numerator[f@ n] - Denominator[f@ n], {n, 76}] (* Michael De Vlieger, Sep 09 2015 *)

PROG

(PARI) a(n) = numerator(ab = sigma(n)/n) - denominator(ab);

CROSSREFS

Cf. A000203, A001065, A014567, A017665, A017666, A053813, A069057.

Sequence in context: A263756 A204984 A335341 * A325969 A325826 A081297

Adjacent sequences: A243470 A243471 A243472 * A243474 A243475 A243476

KEYWORD

nonn

AUTHOR

Michel Marcus, Jun 05 2014

STATUS

approved