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 A261989 #20 Sep 21 2015 06:26:57 %S A261989 1,65,175,20737,32045,41474,64090,128180,207370,207553,352529,415106, %T A261989 705058,1264957,1762645,1824877,2075530,2529914,3525290,3628975, %U A261989 3649754,7050580,7590250,10223341,12649570,17626450,20446682,21504269,23723401,36321775,40893364,43008538,45621925 %N A261989 Numbers such that A017666(n) = A017668(n). %H A261989 Michel Marcus, <a href="/A261989/b261989.txt">Table of n, a(n) for n = 1..61</a> %e A261989 sigma(65,-1) = 84/65 and sigma(65,-2) = 68/65, both having the same denominator, so 65 is a term. %e A261989 sigma(32045, -1) = 9072/6409 and sigma(32045, -2) = 6736/6409, both having the same denominator, so 32045 is a term. %o A261989 (PARI) isok(n) = denominator(sigma(n,-1))==denominator(sigma(n,-2)); %Y A261989 Cf. denominator of sum of powers of divisors of n: A017666 (-1st powers), A017668 (-2nd powers). %K A261989 nonn %O A261989 1,2 %A A261989 _Michel Marcus_, Sep 19 2015