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A322656 Denominator of (Sum_{d|n} sigma(d)) / sigma(n). 2

%I

%S 1,3,4,7,6,3,8,15,13,9,12,28,14,2,24,31,18,13,20,6,32,9,24,6,31,7,20,

%T 56,30,18,32,21,48,27,16,91,38,5,56,45,42,8,44,84,13,18,48,124,19,93,

%U 72,98,54,15,72,20,16,45,60,24,62,8,52,127,4,36,68,126,96

%N Denominator of (Sum_{d|n} sigma(d)) / sigma(n).

%C Denominator of A007429(n) / A000203(n).

%C Also denominator of Sum_{d|n} (sigma(d) / sigma(n)).

%F a(n) = 1 for numbers in A221219.

%e For n = 4; a(4) = denominator((Sum_{d|4} sigma(d)) / sigma(4)) = denominator((1 + 3 + 7) / (1 + 2 + 4)) = denominator(11/7) = 7.

%t Table[Denominator[Sum[DivisorSigma[1, d], {d, Divisors[n]}] / DivisorSigma[1, n]], {n, 1, 100}] (* _Vaclav Kotesovec_, Dec 22 2018 *)

%o (MAGMA) [Denominator(&+[SumOfDivisors(d): d in Divisors(n)] / SumOfDivisors(n)): n in [1..1000]]

%o (PARI) a(n) = denominator(sumdiv(n, d, sigma(d))/sigma(n)); \\ _Michel Marcus_, Dec 22 2018

%Y Cf. A000203, A007429, A319296, A221219, A322655 (numerator).

%K nonn,frac

%O 1,2

%A _Jaroslav Krizek_, Dec 22 2018

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Last modified April 22 10:18 EDT 2019. Contains 322330 sequences. (Running on oeis4.)