G.f.: -(2+7*x-x^3)/(1+4*x-4*x^3-x^4).

Terms

a(0) =-2a(1) =1a(2) =-4a(3) =9a(4) =-34a(5) =121a(6) =-452a(7) =1681a(8) =-6274a(9) =23409a(10) =-87364a(11) =326041a(12) =-1216802a(13) =4541161a(14) =-16947844a(15) =63250209a(16) =-236052994a(17) =880961761a(18) =-3287794052a(19) =12270214441a(20) =-45793063714a(21) =170902040409a(22) =-637815097924