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 A033008 #11 Feb 05 2014 08:09:26
%S A033008 11,22,33,44,55,66,77,88,99,1100,1122,1133,1144,1155,1166,1177,1188,
%T A033008 1199,2200,2211,2233,2244,2255,2266,2277,2288,2299,3300,3311,3322,
%U A033008 3344,3355,3366,3377,3388,3399,4400,4411,4422,4433
%N A033008 Every run of digits of n in base 10 has length 2.
%C A033008 See A043291 and A033001 through A033014 for the analog in other bases, A033015 - A033029 for the variants with run lengths >= 2. - _M. F. Hasler_, Feb 02 2014
%H A033008 Vincenzo Librandi, <a href="/A033008/b033008.txt">Table of n, a(n) for n = 1..800</a>
%F A033008 a(n) = 11*A043314(n) (= 11*n for n<10). - _M. F. Hasler_, Feb 02 2014
%t A033008 Select[Range[10000], Union[Length/@Split[IntegerDigits[#, 10]]]=={2}&] (* _Vincenzo Librandi_, Feb 05 2014 *)
%K A033008 nonn,base
%O A033008 1,1
%A A033008 _Clark Kimberling_