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 A043091 #8 Apr 04 2015 14:18:36
%S A043091 0,1,2,3,4,5,7,8,9,10,11,13,14,15,16,17,19,20,21,22,23,26,27,28,29,35,
%T A043091 36,38,39,40,41,42,44,45,46,47,48,51,52,53,54,55,57,58,59,65,66,67,69,
%U A043091 70,71,72,73,76,77,78,79,80,82,83,84,85,86
%N A043091 Every string of 2 consecutive base 5 digits contains exactly 2 distinct numbers.
%F A043091 A031943 UNION {0}. [From _R. J. Mathar_, Oct 20 2008]
%t A043091 Select[Range[0,100],FreeQ[Differences[IntegerDigits[#,5]],0]&] (* _Harvey P. Dale_, Apr 04 2015 *)
%K A043091 nonn,base
%O A043091 0,3
%A A043091 _Clark Kimberling_