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 A257550 #12 May 11 2015 17:09:39
%S A257550 17907119,18828809,31692569,73421039,179467469,322757819,337567229,
%T A257550 627702389,975314339,2537636009,2722271369,3328653509,3917646809,
%U A257550 5529412349,6369847469,11179199849,11201693579,11363832479,13442120999,16781760449,19751331599,20002320029
%N A257550 Numbers n such that phi(n) = 5*phi(n+1).
%H A257550 Giovanni Resta, <a href="/A257550/b257550.txt">Table of n, a(n) for n = 1..103</a> (terms < 10^12)
%e A257550 phi(17907119) = 16588800 = 5*phi(17907120).
%t A257550 a1={};nmax=10^9;last=EulerPhi[1];n=2;
%t A257550 While[n<nmax,ep=EulerPhi[n];
%t A257550 If[last==5ep,AppendTo[a1,n-1];];
%t A257550 n++;last=ep;];a1 (* _Ray Chandler_, Apr 30 2015 *)
%Y A257550 Cf. A001274, A171262, A256907, A256937.
%K A257550 nonn
%O A257550 1,1
%A A257550 _Ray Chandler_, Apr 29 2015
%E A257550 a(10)-a(22) from _Giovanni Resta_, May 11 2015