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 A204258 #19 Aug 19 2021 02:31:22
%S A204258 1,1,7,54,346,3732,50928,636288,10421856,204446592,3783985632,
%T A204258 84204904320,2154137877504,52813565568000,1488803964595200,
%U A204258 46983956781312000,1434084567201792000,48976637440702464000,1838658764187353088000,67159997418955456512000
%N A204258 Permanent of the n-th principal submatrix of A204257.
%H A204258 Vaclav Kotesovec, <a href="/A204258/b204258.txt">Table of n, a(n) for n = 0..35</a>
%t A204258 f[i_, j_] := 1 + Mod[i + 2 j, 3];
%t A204258 m[n_] := Table[f[i, j], {i, 1, n}, {j, 1, n}]
%t A204258 TableForm[m[8]] (* 8x8 principal submatrix *)
%t A204258 Flatten[Table[f[i, n + 1 - i],
%t A204258 {n, 1, 12}, {i, 1, n}]] (* A204257 *)
%t A204258 Join[{1},Table[Permanent[m[n]], {n, 1, 20}]] (* A204258 *)
%o A204258 (PARI) a(n) = matpermanent(matrix(n, n, i, j, 1 + ((i+2*j) % 3))); \\ _Michel Marcus_, Jan 30 2021
%Y A204258 Cf. A204257.
%K A204258 nonn
%O A204258 0,3
%A A204258 _Clark Kimberling_, Jan 14 2012
%E A204258 a(0) and a(19) from _Pontus von Brömssen_, Jan 30 2021