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 A140663 #9 Jul 13 2015 21:08:15
%S A140663 2,0,7,1,9,6,9,2,2,9,0,8,2,3,1,2,9,1,5,2,3,4,1,9,0,5,5,6,3,6,3,2,9,5,
%T A140663 7,7,7,8,5,3,5,3,3,8,0,7,5,9,5,4,1,1,6,2,2,7,1,7,4,9,0,8,1,8,3,9,4,6,
%U A140663 6,6,1,0,9,8,5,2,7,7,3,4,0,0,6,9,0,0,6,6,5,7,7,5,4,6,3,0,9,8,5,3,8,5,4,6,2
%N A140663 Decimal expansion of the number x defined by x^(x^x) = 27.
%e A140663 2.07196922908231...
%p A140663 Digits := 120: x := 2.071 : for i from 1 to 30 do xxx := x^(x^x) : n := xxx-27 : d := xxx*(x^x*log(x)*(1+log(x))+x^(x-1)) ; x := evalf(x-n/d) ; print(x) ; od: # _R. J. Mathar_, Aug 08 2008
%t A140663 digits = 105; x0 = x /. FindRoot[x^(x^x) == 27, {x, 2}, WorkingPrecision -> digits+1]; RealDigits[x0, 10, digits][[1]] (* _Jean-François Alcover_, Jan 28 2014 *)
%Y A140663 Cf. A093590.
%K A140663 cons,nonn
%O A140663 1,1
%A A140663 _Joshua Taylor_, Jul 11 2008
%E A140663 Extended beyond 15 digits by _R. J. Mathar_, Aug 08 2008