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A318060
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a(n) is the denominator of sigma(sigma(n))/n.
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7
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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
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1,3
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LINKS
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EXAMPLE
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For n=2, sigma(sigma(n)) = 4, so a(2) = 1.
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MAPLE
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seq(denom((numtheory:-sigma@@2)(n)/n), n=1..200); # Robert Israel, Aug 15 2018
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MATHEMATICA
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Table[(DivisorSigma[1, DivisorSigma[1, n]])/n, {n, 70}]//Denominator (* Harvey P. Dale, Mar 30 2023 *)
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PROG
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(PARI) a(n) = denominator(sigma(sigma(n))/n);
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CROSSREFS
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KEYWORD
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nonn,frac
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AUTHOR
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STATUS
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approved
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