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 A050733 #5 Oct 16 2019 01:14:16 %S A050733 1,3,9,27,81,243,729,2187,6561,19683,59049,1594323,4782969,14348907, %T A050733 43046721,129140163,387420489,10460353203,31381059609,282429536481, %U A050733 2541865828329,109418989131512359209,30903154382632612361920641803529 %N A050733 Numbers of form 3^k (values of k see A050724) containing no pair of consecutive equal digits (probably finite). %Y A050733 Cf. A043096, A050724. %K A050733 nonn,base %O A050733 0,2 %A A050733 _Patrick De Geest_, Sep 15 1999