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 A318060 a(n) is the denominator of sigma(sigma(n))/n. 6
 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 (list; graph; refs; listen; history; text; internal format)
 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 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: A030101 A162742 A081432 * A336652 A136655 A060819 Adjacent sequences:  A318057 A318058 A318059 * A318061 A318062 A318063 KEYWORD nonn,frac AUTHOR Michel Marcus, Aug 14 2018 STATUS approved

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Last modified September 20 11:01 EDT 2020. Contains 337264 sequences. (Running on oeis4.)