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 A204440 #22 Jan 31 2021 10:24:32
%S A204440 1,1,1,2,6,20,80,384,2016,12096,82080,597888,4783104,41886720,
%T A204440 389145600,3891456000,41803776000,472283136000,5667397632000,
%U A204440 72153317376000,959814696960000,13437405757440000,197840194965504000,3028176742219776000,48450827875516416000
%N A204440 Permanent of the n-th principal submatrix of A204439.
%C A204440 Also the number of permutations pi in S_n such that pi(i) + i != 1 (mod 3) for all i. - _Peter Kagey_, Jan 25 2021
%t A204440 f[i_, j_] := Mod[(2 + i + j)^2, 3];
%t A204440 m[n_] := Table[f[i, j], {i, 1, n}, {j, 1, n}]
%t A204440 TableForm[m[8]] (* 8x8 principal submatrix *)
%t A204440 Flatten[Table[f[i, n + 1 - i],
%t A204440 {n, 1, 14}, {i, 1, n}]] (* A204439 *)
%t A204440 Join[{1},Table[Permanent[m[n]], {n, 1, 22}]] (* A204440 *)
%Y A204440 Cf. A204239, A204435.
%K A204440 nonn
%O A204440 0,4
%A A204440 _Clark Kimberling_, Jan 15 2012
%E A204440 Typo in name corrected by _Michel Marcus_, Nov 11 2016
%E A204440 a(0) and a(23)-a(24) from _Pontus von Brömssen_, Jan 29 2021