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A173789 a(n) is the number of (0,1)- matrices A=(a_{ij}) of size n X (3n) such each row has exactly three 1's and each column has exactly one 1 and with the restriction that no 1 stands on the diagonal from a_{11} to a_{22}. 0

%I

%S 0,6,540,123480,57405600,47488518000,63760174077600,

%T 129947848862832000,382114148130658944000,1557871091922736150560000,

%U 8528480929388117171073600000,61063236793210618551364940160000

%N a(n) is the number of (0,1)- matrices A=(a_{ij}) of size n X (3n) such each row has exactly three 1's and each column has exactly one 1 and with the restriction that no 1 stands on the diagonal from a_{11} to a_{22}.

%F a(n)= sum_{k=0..n} (-1)^k (3n-k)!/(6^{n-k}*2^k) * binomial(n,k).

%o (PARI) a(n)= sum(k=0, n, (-1)^k *(3*n-k)! /(6^(n-k)*2^k) * binomial(n,k)) \\ _Michel Marcus_, Jul 25 2013

%K nonn

%O 1,2

%A _Shanzhen Gao_, Feb 24 2010

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Last modified February 16 04:34 EST 2019. Contains 320140 sequences. (Running on oeis4.)