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Numbers n such that sigma(n)/tau(n) has denominator 5.
1

%I #15 Sep 08 2022 08:45:05

%S 16,48,80,81,112,176,208,240,272,336,368,405,496,528,560,567,592,624,

%T 625,656,688,720,752,784,816,848,880,891,976,1040,1053,1072,1104,1134,

%U 1136,1168,1232,1328,1360,1377,1456,1488,1536,1552,1584,1616,1620,1648

%N Numbers n such that sigma(n)/tau(n) has denominator 5.

%H Amiram Eldar, <a href="/A069084/b069084.txt">Table of n, a(n) for n = 1..10000</a>

%F n such that A057021(n)=5

%t Select[Range[500], Denominator[DivisorSigma[1, #]/DivisorSigma[0, #]] == 5 &] (* _Amiram Eldar_, Sep 08 2019 *)

%o (Magma) [n:n in [1..1700]|Denominator(SumOfDivisors(n)/#Divisors(n)) eq 5]; // _Marius A. Burtea_, Sep 08 2019

%Y Cf. A000005, A000203, A057021.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Apr 05 2002