Let J_n be nXn n X n matrix which contains 1's only, I=I_n be the nXn n X n identity matrix and P=P_n be the incidence matrix of the cycle (2,3,...,n,1). Then a(n) is the number of (0,1) nXn n X n matrices A<=J_n-I-P with exactly two 1's in every row and column
editing
approved
_Vladimir Shevelev (shevelev(AT)bgu.ac.il), _, Mar 22 2010
Let J_n be nXn matrix which contains 1's only, I=I_n be the nXn identity matrix and P=P_n be the incidence matrix of the cycle (2,3,...,n,1). Then a(n) is the number of (0,1) nXn matrices A<=J_n-I-P with exactly two 1's in every row and column
0, 1, 13, 522, 27828, 1867363
3,3
V. S. Shevelev, Development of the rook technique for calculating the cyclic indicators of (0,1)-matrices, Izvestia Vuzov of the North-Caucasus region, Nature sciences 4 (1996), 21-28 (in Russian).
S. E. Grigorchuk, V. S. Shevelev, An algorithm of computing the cyclic indicator of couples discordant permutations with restricted position, Izvestia Vuzov of the North-Caucasus region, Nature sciences 3 (1997), 5-13 (in Russian).
nonn,uned
Vladimir Shevelev (shevelev(AT)bgu.ac.il), Mar 22 2010
approved