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 A097002 #4 Oct 15 2013 22:32:33
%S A097002 1,3,7,15,31,63,127,255,511,1023,2047,4095,8191,6045,24552,65535,
%T A097002 131071,262143,524287,1048575,2097151,4194303,8388607,16777215,
%U A097002 33554431,67108863,134217727,268435455,536870911,1073741823
%N A097002 A062402(x)=sigma(phi[x]) function is iterated; initial value=2^n; a(n)=smallest term of trajectory.
%e A097002 n=13: 2^n=8192, trajectory ={8192, 8191, 26208, [20440], 20440, .. a[13]=8191 arose in transient.
%t A097002 gf[x_] :=DivisorSigma[1, EulerPhi[x]] gite[x_, hos_] :=NestList[gf, x, hos] Table[Min[gite[2^w, 200]], {w, 1, 30}]
%Y A097002 Cf. A000010, A000203, A062402, A096857.
%K A097002 nonn
%O A097002 1,2
%A A097002 _Labos Elemer_, Jul 21 2004