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 A049117 #22 Oct 15 2013 22:30:26
%S A049117 3,7,19,47,163,487,1307,2879,19683,39367,177147,531441,1594323,
%T A049117 4782969,14348907,43046721,86093443,258280327,688747547,3486784401,
%U A049117 10460353203
%N A049117 Smallest number which when Euler phi function is repeatedly applied have not reached a power of 2 in n steps.
%C A049117 a(21) <= 31381059609 = 3^22. [_Donovan Johnson_, Feb 06 2010]
%C A049117 Note that all terms so far are primes or powers of 3. Is it true that all terms have this form? - _T. D. Noe_, Oct 07 2013
%e A049117 The corresponding iterated phi-sequences are:
%e A049117 {3, 2, 1},
%e A049117 {7, 6, 2, 1},
%e A049117 {19, 18, 6, 2, 1},
%e A049117 {47, 46, 22, 10, 4, 2, 1},
%e A049117 {163, 162, 54, 18, 6, 2, 1},
%e A049117 {487, 486, 162, 54, 18, 6, 2, 1}, ...
%t A049117 a[n_] := Module[{i = 1}, While[IntegerQ[Log[2, Nest[EulerPhi, i, n]]], i++ ]; i]; (* Sam Handler (sam_5_5_5_0(AT)yahoo.com), Sep 04 2006 *)
%Y A049117 A variant of A227946.
%Y A049117 Cf. A000010.
%K A049117 nonn,more
%O A049117 0,1
%A A049117 _Labos Elemer_
%E A049117 More terms from _Jud McCranie_, Jan 14 2000
%E A049117 More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Sep 04 2006
%E A049117 a(19)-a(20) from _Donovan Johnson_, Feb 06 2010