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 A031945 #7 May 01 2013 21:06:45 %S A031945 75,78,99,108,114,120,135,141,147,156,177,180,198,201,210,216,225,228, %T A031945 267,270,283,286,291,295,299,300,301,302,303,306,310,312,313,314,315, %U A031945 318,331,334,355,364,370,376,387,391,395,396 %N A031945 Numbers in which 0,1,2,3 all occur in base 4. %C A031945 Or, numbers in which the number of distinct base 4 digits is 4. %K A031945 nonn,base %O A031945 1,1 %A A031945 _Clark Kimberling_ %E A031945 Edited by _N. J. A. Sloane_, Apr 05 2009 at the suggestion of R. J. Mathar