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 A015707 #23 Dec 05 2018 18:37:51
%S A015707 1,6,18,24,28,40,54,72,96,117,135,196,200,216,224,288,360,384,468,496,
%T A015707 600,640,756,775,864,891,1000,1080,1152,1372,1488,1521,1568,1701,1792,
%U A015707 1944,2016,2160,2176,2480,2592,3100,3159,3200,3375,3456,3744,4320,4455,4608
%N A015707 Values of n where (phi(n) * sigma(n))/n is an integer and increases.
%C A015707 This sequence is infinite since there are infinitely many numbers m with an arbitrarily large integer value of (phi(m) * sigma(m))/m. For example, if m = 2 * 3^k, then this value is (3^(k+1)-1)/2. - _Amiram Eldar_, Dec 05 2018
%H A015707 Richard K. Guy, <a href="https://www.jstor.org/stable/2974586">Divisors and desires</a>, Amer. Math. Monthly, 104 (1997), 359-360.
%t A015707 seq = {}; rm = 0; Do[r = EulerPhi[n]*DivisorSigma[1, n]/n; If[IntegerQ[r] && r > rm, rm = r; AppendTo[seq, n]], {n, 1, 5000}]; seq (* _Amiram Eldar_, Dec 05 2018 *)
%Y A015707 Cf. A015706.
%K A015707 nonn
%O A015707 1,2
%A A015707 _Robert G. Wilson v_
%E A015707 Title improved by _Sean A. Irvine_, Dec 05 2018
%E A015707 a(1)=1 inserted and more terms added by _Amiram Eldar_, Dec 05 2018