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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The permutations of rows i anf 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.

LINKS

Table of n, a(n) for n=1..6.

Wouter Meeussen, Periodic Matrices

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 by 6 matrices.

MATHEMATICA

see link.

CROSSREFS

Cf. A072148, A111485.

Sequence in context: A259859 A298940 A327847 * A149048 A149049 A149050

Adjacent sequences:  A111746 A111747 A111748 * A111750 A111751 A111752

KEYWORD

hard,nonn

AUTHOR

Wouter Meeussen, Nov 19 2005

STATUS

approved

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Last modified October 27 20:18 EDT 2021. Contains 348290 sequences. (Running on oeis4.)