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 A202820 #6 Mar 30 2012 16:52:08 %S A202820 0,0,0,1,1,1,3,2,1,0,17,20,22,23,23,105,88,68,46,23,0 %N A202820 The left-hand half-triangle of A202704. %e A202820 Triangle begins: %e A202820 0 %e A202820 0 0 %e A202820 1 1 1 %e A202820 3 2 1 0 %e A202820 17 20 22 23 23 %e A202820 105 88 68 46 23 0 %Y A202820 Cf. A202704, A202819. %K A202820 nonn,tabl,more %O A202820 1,7 %A A202820 _N. J. A. Sloane_, Dec 25 2011