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 A136041 #6 Jan 06 2015 03:47:01
%S A136041 3,7,19,43,163,487,1459,3079,8803,39367,78787,196831,581743,2125819,
%T A136041 6381667,19131877,86093443,258280327,516560659,1214874127
%N A136041 Largest prime p such that phi^n(p) = 2, where phi^n means n iterations of Euler's totient function.
%C A136041 The largest prime in row n+1 of A058812. From Shapiro, we know that a(n) <= 1 + 2*3^(n-1). This bound is attained for n=1,2,3,5,6,7,17,18,.., which is n=A003306(k)+1 for k=1,2,3,...
%H A136041 Harold Shapiro, <a href="http://www.jstor.org/stable/2303988">An arithmetic function arising from the phi function</a>, Amer. Math. Monthly, Vol. 50, No. 1 (1943), 18-30.
%t A136041 nn=20; pk=Table[0,{nn}]; Do[p=Prime[n]; k=Length[NestWhileList[EulerPhi,p,#>2&]]-1; If[0<k<=nn, pk[[k]]=p], {n,PrimePi[1+2*3^(nn-1)]}]; pk
%K A136041 nonn,more
%O A136041 1,1
%A A136041 _T. D. Noe_, Dec 12 2007