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 A067500 #9 Dec 05 2013 19:55:09
%S A067500 1,3,9,27,81,243,19683,59049,177147,1594323,43046721,129140163,
%T A067500 10460353203,7625597484987,617673396283947,50031545098999707,
%U A067500 150094635296999121,4052555153018976267
%N A067500 Powers of 3 with digit sum also a power of 3.
%C A067500 a(n) = 3^A118872(n).
%t A067500 With[{l3s=3^Range[0,200]},Select[l3s,MemberQ[l3s,Total[IntegerDigits[ #]]]&]] (* _Harvey P. Dale_, May 20 2011 *)
%Y A067500 Cf. A067499.
%Y A067500 Cf. A004166, A000244.
%K A067500 base,easy,nonn
%O A067500 1,2
%A A067500 _Amarnath Murthy_, Feb 11 2002
%E A067500 More terms from _Harvey P. Dale_, Mar 02 2002
%E A067500 Offset corrected by _Reinhard Zumkeller_, May 14 2011