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 A014419 #5 Mar 30 2012 17:20:36 %S A014419 0,1,3,4,6,9,10,12,13,15,18,19,21,22,27,28,30,31,33,36,37,39,40,42,45, %T A014419 46,48,49,54,55,57,58,60,63,64,66,67,69,72,73,75,76,81,82,84,85,87,90, %U A014419 91,93,94,96,99,100,102,103,108,109,111,112,114,117,118,120 %N A014419 Write n in base of Catalan numbers, then interpret as if written in base 3. %Y A014419 Cf. A014418. %K A014419 nonn,easy %O A014419 0,3 %A A014419 _Olivier Gérard_