400448833106domain: NAppears in sequencesNumber of perfect matchings in the graph C_9 X C_{2n}.at n=3A281583Number of perfect matchings in the graph C_10 X C_n.at n=6A281679a(n) = ( Product_{j=1..n} Product_{k=1..n+1} (4*sin((2*j-1)*Pi/n)^2 + 4*sin((2*k-1)*Pi/(n+1))^2) )^(1/4).at n=9A341493