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 A216216 #7 Mar 14 2013 15:02:18
%S A216216 1,1,1,1,2,1,0,3,3,0,0,3,6,3,0,0,0,9,9,0,0,0,0,9,18,9,0,0,0,0,0,27,27,
%T A216216 0,0,0,0,0,0,27,54,27,0,0,0,0,0,0,0,81,81,0,0,0,0,0,0,0,0,81,162,81,0,
%U A216216 0,0,0
%N A216216 Square array T, read by antidiagonals: T(n,k) = 0 if n-k>=3 or if k-n>=3, T(2,0) = T(1,0) = T(0,0) = T(0,1) = T(0,2) = 1, T(n,k) = T(n-1,k) + T(n,k-1).
%F A216216 T(n,n) = A025192(n).
%F A216216 T(n+1,n) = T(n+2,n) = T(n,n+1) = T(n,n+2) = 3^n = A000244(n).
%F A216216 Sum_{k, 0<=k<=n} T(n-k,k) = A068911(n).
%e A216216 Square array begins:
%e A216216 1, 1, 1, 0, 0, 0, 0, 0, 0, ... n = 0
%e A216216 1, 2, 3, 3, 0, 0, 0, 0, 0, ... n = 1
%e A216216 1, 3, 6, 9, 9, 0, 0, 0, 0, ... n = 2
%e A216216 0, 3, 9, 18, 27, 27, 0, 0, 0, ... n = 3
%e A216216 0, 0, 9, 27, 54, 81, 81, 0, 0, ... n = 4
%e A216216 0, 0, 0, 27, 81, 162, 243, 243, 0, ... n = 5
%e A216216 ....
%Y A216216 Cf. A000244, A025192, A068911, A068913
%K A216216 nonn,tabl
%O A216216 0,5
%A A216216 _Philippe Deléham_, Mar 13 2013