880961761domain: NAppears in sequencesNumber of perfect matchings (or domino tilings) in C_4 X P_n.at n=16A006253Indices of octagonal numbers which are also squares.at n=8A046184G.f.: -(2+7*x-x^3)/(1+4*x-4*x^3-x^4).at n=17A097949