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%I #17 Mar 30 2012 18:52:59
%S 1,1,2,4,8,18
%N Number of different values of the permanent of an n X n (0,1)-matrix with exactly three 1's in each row and each column.
%C The values a(n) are unknown for n>=9.
%D V. I. Bolshakov, On spectrum of permanent on Lambda_n^k, Proc. of Seminar on Discrete Math. and Appl., Moscow State Univ. (1986), 65-73 (in Russian).
%H V. S. Shevelev, <a href="http://dx.doi.org/10.1007/BF01104103">Some problems of the theory of enumerating the permutations with restricted position</a>, Journal of Soviet Mathematics, 61 (4) (1992) 2272-2317 (see pp. 2307-2309).
%Y Cf. A185177 (values of the permanent), A176211, A176212.
%K nonn,bref,hard,more
%O 3,3
%A _Vladimir Shevelev_, Feb 19 2011