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 A057021 Denominator of (sum of divisors of n / number of divisors of n). 20
 1, 2, 1, 3, 1, 1, 1, 4, 3, 2, 1, 3, 1, 1, 1, 5, 1, 2, 1, 1, 1, 1, 1, 2, 3, 2, 1, 3, 1, 1, 1, 2, 1, 2, 1, 9, 1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 5, 1, 2, 1, 3, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 3, 7, 1, 1, 1, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) = 1 when n is listed in A003601, a(n) > 1 when n is listed in A049642. - Alonso del Arte, Jan 31 2006 a(A069081(n)) = 2. - Bernard Schott, Sep 19 2019 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A057020(n)*A000005(n)/A000203(n) = A000005(n)/A009205(n). EXAMPLE a(12)=3 since the 6 divisors of 12 are 1, 2, 3, 4, 6 and 12 and 1+2+3+4+6+12=28 and 28/6=14/3. MAPLE with(numtheory): seq(denom(sigma(n)/tau(n)), n=1..70) ; # Zerinvary Lajos, Jun 04 2008 MATHEMATICA Denominator[Table[(Plus @@ Divisors[n])/Length[Divisors[n]], {n, 70}]] (* Alonso del Arte, Feb 24 2006 *) PROG (Haskell) import Data.Ratio ((%), denominator) a057021 n = denominator \$ a000203 n % a000005 n -- Reinhard Zumkeller, Jan 06 2012 (PARI) a(n) = denominator(sigma(n)/numdiv(n)); \\ Michel Marcus, Apr 12 2016 (Magma) [Denominator(SumOfDivisors(n)/#Divisors(n)):n in [1..100]]; // Marius A. Burtea, Sep 08 2019 CROSSREFS Cf. A000005, A000203, A009205, A054025, A057020 (numerator), A057022, A069081. Sequence in context: A353278 A328917 A265917 * A152443 A119804 A300977 Adjacent sequences: A057018 A057019 A057020 * A057022 A057023 A057024 KEYWORD frac,nonn AUTHOR Henry Bottomley, Jul 21 2000 STATUS approved

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Last modified September 30 06:20 EDT 2023. Contains 365781 sequences. (Running on oeis4.)