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 A056560 #7 Jul 11 2015 00:16:10 %S A056560 0,0,1,0,0,1,0,2,1,0,0,1,0,2,1,0,3,2,1,0,0,1,0,2,1,0,3,2,1,0,4,3,2,1, %T A056560 0,0,1,0,2,1,0,3,2,1,0,4,3,2,1,0,5,4,3,2,1,0,0,1,0,2,1,0,3,2,1,0,4,3, %U A056560 2,1,0,5,4,3,2,1,0,6,5,4,3,2,1,0,0,1,0,2,1,0,3,2,1,0,4,3,2,1,0,5,4,3,2,1,0 %N A056560 Tetrahedron with T(t,n,k)=n-k; succession of growing finite triangles with increasing values towards bottom left. %F A056560 a(n) = A056557(n) - A056558(n). %e A056560 First triangle: [0]; second triangle: [0; 1 0]; third triangle: [0; 1 0; 2 1 0]; ... %Y A056560 Together with A056558 and A056559 might enable reading "by antidiagonals" of cube arrays as 3-dimensional analog of A002262 and A025581 with square arrays. %K A056560 nonn %O A056560 0,8 %A A056560 _Henry Bottomley_, Jun 26 2000