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 A039652 #17 Aug 31 2017 23:18:03
%S A039652 2,1,15,35,69,255,535,949,1957,2513,2923,4531,17701,22957,54589,79421,
%T A039652 80029,84493,98581,102827,115243,239111,291149,310813,362621,398893,
%U A039652 598341,801923,838307,1063493,1079833,1123813,1311121,1329403,1582439
%N A039652 Becomes prime after n iterations of f(x) = phi(x)+1 (least inverse of A039651).
%C A039652 Of the terms n <= 66, all are semiprimes except those for n = 0, 1, 5, and 19. Why? - _T. D. Noe_, Oct 17 2013
%H A039652 T. D. Noe, <a href="/A039652/b039652.txt">Table of n, a(n) for n = 0..66</a>
%t A039652 nn = 34; t = Table[0, {nn}]; found = 0; n = 0; While[found < nn, n++; len = Length[NestWhileList[EulerPhi[#] + 1 &, n, UnsameQ, All]] - 2; If[len <= nn && t[[len]] == 0, t[[len]] = n; found++]]; t = Join[{2}, t] (* _T. D. Noe_, Oct 17 2013 *)
%Y A039652 Cf. A039649, A039650, A039651, A039652, A039653, A039654, A039655, A039656.
%K A039652 nonn,hard
%O A039652 0,1
%A A039652 _David W. Wilson_