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 A145676 Number of n X n {0,-1,1}-matrices A such that permanent( |A| ) = det A, where |A| is obtained from A by taking the absolute value of each entry. 2

%I

%S 1,2,49,8419,9162049

%N Number of n X n {0,-1,1}-matrices A such that permanent( |A| ) = det A, where |A| is obtained from A by taking the absolute value of each entry.

%e Here are the 2 for the 1 X 1 case:

%e {{{0}}, {{1}}}

%e and the 49 for the 2 X 2 case:

%e {{{-1, -1}, {0, -1}}, {{-1, -1}, {0, 0}}, {{-1, -1}, {1, -1}}, {{-1, -1}, {1, 0}},

%e {{-1, 0}, {-1, -1}}, {{-1, 0}, {-1, 0}}, {{-1, 0}, {0, -1}}, {{-1, 0}, {0, 0}},

%e {{-1, 0}, {1, -1}}, {{-1, 0}, {1, 0}}, {{-1, 1}, {-1, -1}}, {{-1, 1}, {-1, 0}},

%e {{-1, 1}, {0, -1}}, {{-1, 1}, {0, 0}}, {{0, -1}, {0, -1}}, {{0, -1}, {0, 0}},

%e {{0, -1}, {0, 1}}, {{0, -1}, {1, -1}}, {{0, -1}, {1, 0}}, {{0, -1}, {1, 1}},

%e {{0, 0}, {-1, -1}}, {{0, 0}, {-1, 0}}, {{0, 0}, {-1, 1}}, {{0, 0}, {0, -1}},

%e {{0, 0}, {0, 0}}, {{0, 0}, {0, 1}}, {{0, 0}, {1, -1}}, {{0, 0}, {1, 0}},

%e {{0, 0}, {1, 1}}, {{0, 1}, {-1, -1}}, {{0, 1}, {-1, 0}}, {{0, 1}, {-1, 1}},

%e {{0, 1}, {0, -1}}, {{0, 1}, {0, 0}}, {{0, 1}, {0, 1}}, {{1, -1}, {0, 0}},

%e {{1, -1}, {0, 1}}, {{1, -1}, {1, 0}}, {{1, -1}, {1, 1}}, {{1, 0}, {-1, 0}},

%e {{1, 0}, {-1, 1}}, {{1, 0}, {0, 0}}, {{1, 0}, {0, 1}}, {{1, 0}, {1, 0}},

%e {{1, 0}, {1, 1}}, {{1, 1}, {-1, 0}}, {{1, 1}, {-1, 1}}, {{1, 1}, {0, 0}}, {{1, 1}, {0, 1}}}

%Y Cf. A145675.

%K nonn

%O 0,2

%A _Eric W. Weisstein_, Mar 26 2009

%E a(4) from _Eric W. Weisstein_, Mar 27 2009

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)