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%I #19 Sep 08 2022 08:45:05
%S 2,10,18,24,26,32,34,50,58,74,82,88,90,98,106,120,122,130,146,152,160,
%T 170,178,194,202,216,218,226,234,242,250,274,288,290,298,306,312,314,
%U 338,344,346,362,370,386,394,408,410,416,440,442,458,466,472,482,490
%N Numbers n such that sigma(n)/tau(n) has denominator 2.
%H Amiram Eldar, <a href="/A069081/b069081.txt">Table of n, a(n) for n = 1..10000</a>
%F n such that A057021(n)=2.
%t Select[Range[500], Denominator[DivisorSigma[1, #]/DivisorSigma[0, #]] == 2 &] (* _Amiram Eldar_, Sep 08 2019 *)
%o (Magma) [n:n in [1..500]|Denominator(SumOfDivisors(n)/#Divisors(n)) eq 2]; // _Marius A. Burtea_, Sep 08 2019
%Y Cf. A000005, A000203, A057021.
%K easy,nonn
%O 1,1
%A _Benoit Cloitre_, Apr 05 2002
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