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 A174820 #2 Mar 31 2012 20:55:21 %S A174820 1,-3,1,-1,-2,1,-1,-1,-2,1,-1,0,0,-2,1,-1,-1,-1,0,-2,1,-1,0,0,0,0,-2, %T A174820 1,-1,-1,0,-1,0,0,-2,1,-1,0,-1,0,0,0,0,-2,1,-1,-1,0,0,-1,0,0,0,-2,1, %U A174820 -1,0,0,0,0,0,0,0,0,-2,1,-1,-1,-1,-1,0,-1,0,0,0,0,-2,1,-1,0,0,0,0,0,0,0,0,0 %N A174820 Triangle T(n,k) read by rows. T(n,k) = A174557(n,k)-A174557(n-1,k). %e A174820 Table begins: %e A174820 .1 %e A174820 -3..1 %e A174820 -1.-2..1 %e A174820 -1.-1.-2..1 %e A174820 -1..0..0.-2..1 %e A174820 -1.-1.-1..0.-2..1 %e A174820 -1..0..0..0..0.-2..1 %e A174820 -1.-1..0.-1..0..0.-2..1 %e A174820 -1..0.-1..0..0..0..0.-2..1 %e A174820 -1.-1..0..0.-1..0..0..0.-2..1 %K A174820 sign,tabl %O A174820 1,2 %A A174820 Mats Granvik, _Paul D. Hanna_, Mar 30 2010