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 A111749 #13 Aug 08 2025 03:47:33
%S A111749 1,3,10,39,121,405
%N A111749 Number of (-1,0,1) periodic irreducible matrices (with Tij = -Tji for i < j) up to sign change, transposition and row and column permutations.
%C A111749 The permutations of rows i and j, followed by those of column i and j, preserve the property that (Tij = -Tji for i < j). The periods of the 405 6 X 6 matrices are: 11 times period 3, 94 times period 4, 71 times period 6 and 229 times period 12.
%H A111749 Wouter Meeussen, <a href="http://users.pandora.be/Wouter.Meeussen/PseudoAntiSymmetricMatrixPowers.nb">Periodic Matrices</a>. [broken link]
%e A111749 {{-1,-1,0,0,0,0}, {1,1,-1,0,0,0}, {0,1,-1,0,0,0}, {0,0,0,-1,-1,0}, {0,0,0,1,1,-1}, {0,0,0,0,1,-1}} is one of the 6 X 6 matrices.
%t A111749 (* See link. *)
%Y A111749 Cf. A072148, A111485.
%K A111749 nonn,hard,more
%O A111749 1,2
%A A111749 _Wouter Meeussen_, Nov 19 2005