A318060 - OEIS

A318060

a(n) is the denominator of sigma(sigma(n))/n.

1, 1, 3, 1, 5, 3, 7, 1, 9, 10, 11, 3, 13, 7, 1, 1, 17, 9, 19, 5, 1, 22, 23, 1, 25, 13, 3, 7, 29, 2, 31, 4, 33, 17, 35, 9, 37, 19, 13, 20, 41, 1, 43, 11, 15, 46, 47, 3, 49, 25, 17, 52, 53, 3, 11, 7, 19, 29, 59, 1, 61, 31, 3, 1, 65, 66, 67, 17, 23, 70

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OFFSET

1,3

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

For n=2, sigma(sigma(n)) = 4, so a(2) = 1.

MAPLE

seq(denom((numtheory:-sigma@@2)(n)/n), n=1..200); # Robert Israel, Aug 15 2018

MATHEMATICA

Table[(DivisorSigma[1, DivisorSigma[1, n]])/n, {n, 70}]//Denominator (* Harvey P. Dale, Mar 30 2023 *)

PROG

(PARI) a(n) = denominator(sigma(sigma(n))/n);

CROSSREFS

Cf. A000203 (sigma), A051027.

Cf. A019278 (where a(n) = 1), A318059 (numerator).

Sequence in context: A162742 A348363 A081432 * A336652 A136655 A376427

Adjacent sequences: A318057 A318058 A318059 * A318061 A318062 A318063

KEYWORD

nonn,frac

AUTHOR

Michel Marcus, Aug 14 2018

STATUS

approved