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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.
0
1, 3, 10, 39, 121, 405
OFFSET
1,2
COMMENTS
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.
EXAMPLE
{{-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.
MATHEMATICA
See link.
CROSSREFS
Sequence in context: A259859 A298940 A327847 * A149048 A149049 A149050
KEYWORD
nonn,hard,more
AUTHOR
Wouter Meeussen, Nov 19 2005
STATUS
approved