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%I #7 Sep 08 2022 08:46:21
%S 1,3,4,21,6,12,8,35,52,18,12,12,14,8,24,1085,18,156,20,126,32,36,24,
%T 20,186,14,520,56,30,72,32,9765,48,54,16,1092,38,4,8,210,42,32,44,252,
%U 312,72,48,620,456,558,72,98,54,312,72,56,80,18,60,72,62,32,416
%N a(n) = denominator of Sum_{d|n} (d/sigma(d)) where sigma(k) = the sum of the divisors of k (A000203).
%C Sum_{d|n} (d/sigma(d)) >= 1 for all n >= 1.
%F a(p) = p + 1 for primes p.
%e Sum_{d|n} (d/sigma(d)) for n >= 1: 1, 5/3, 7/4, 47/21, 11/6, 35/12, 15/8, 97/35, 127/52, 55/18, 23/12, 47/12, 27/14, ...
%e For n=4; Sum_{d|4} (d/sigma(d)) = 1/sigma(1) + 2/sigma(2) + 4/sigma(4) = 1/1 + 2/3 + 4/7 = 47/21; a(4) = 21.
%o (Magma) [Denominator(&+[d / SumOfDivisors(d): d in Divisors(n)]): n in [1..100]]
%o (PARI) a(n) = denominator(sumdiv(n, d, d/sigma(d))); \\ _Michel Marcus_, Mar 03 2019
%Y Cf. A000203, A306649 (numerators).
%K nonn,frac
%O 1,2
%A _Jaroslav Krizek_, Mar 03 2019