This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A069081 #19 Sep 08 2022 08:45:05 %S A069081 2,10,18,24,26,32,34,50,58,74,82,88,90,98,106,120,122,130,146,152,160, %T A069081 170,178,194,202,216,218,226,234,242,250,274,288,290,298,306,312,314, %U A069081 338,344,346,362,370,386,394,408,410,416,440,442,458,466,472,482,490 %N A069081 Numbers n such that sigma(n)/tau(n) has denominator 2. %H A069081 Amiram Eldar, <a href="/A069081/b069081.txt">Table of n, a(n) for n = 1..10000</a> %F A069081 n such that A057021(n)=2. %t A069081 Select[Range[500], Denominator[DivisorSigma[1, #]/DivisorSigma[0, #]] == 2 &] (* _Amiram Eldar_, Sep 08 2019 *) %o A069081 (Magma) [n:n in [1..500]|Denominator(SumOfDivisors(n)/#Divisors(n)) eq 2]; // _Marius A. Burtea_, Sep 08 2019 %Y A069081 Cf. A000005, A000203, A057021. %K A069081 easy,nonn %O A069081 1,1 %A A069081 _Benoit Cloitre_, Apr 05 2002