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 A204257 #7 Mar 30 2012 18:58:08
%S A204257 1,3,2,2,1,3,1,3,2,1,3,2,1,3,2,2,1,3,2,1,3,1,3,2,1,3,2,1,3,2,1,3,2,1,
%T A204257 3,2,2,1,3,2,1,3,2,1,3,1,3,2,1,3,2,1,3,2,1,3,2,1,3,2,1,3,2,1,3,2,2,1,
%U A204257 3,2,1,3,2,1,3,2,1,3,1,3,2,1,3,2,1,3,2,1,3,2,1,3,2,1,3,2,1,3,2
%N A204257 Matrix given by f(i,j)=1+[(i+2j) mod 3], by antidiagonals.
%e A204257 Northwest corner:
%e A204257 1 3 2 1 3 2 1 3
%e A204257 2 1 3 2 1 3 2 1
%e A204257 3 2 1 3 2 1 3 2
%e A204257 1 3 2 1 3 2 1 3
%e A204257 2 1 3 2 1 3 2 1
%e A204257 3 2 1 3 2 1 3 2
%t A204257 f[i_, j_] := 1 + Mod[i + 2 j, 3];
%t A204257 m[n_] := Table[f[i, j], {i, 1, n}, {j, 1, n}]
%t A204257 TableForm[m[8]] (* 8x8 principal submatrix *)
%t A204257 Flatten[Table[f[i, n + 1 - i],
%t A204257 {n, 1, 12}, {i, 1, n}]] (* A204257 *)
%t A204257 Permanent[m_] :=
%t A204257 With[{a = Array[x, Length[m]]},
%t A204257 Coefficient[Times @@ (m.a), Times @@ a]];
%t A204257 Table[Permanent[m[n]], {n, 1, 20}] (* A204258 *)
%Y A204257 Cf. A204258.
%K A204257 nonn,tabl
%O A204257 1,2
%A A204257 _Clark Kimberling_, Jan 14 2012