a(n) = 4^n*(1-2*n).

Terms

a(0) =1a(1) =-4a(2) =-48a(3) =-320a(4) =-1792a(5) =-9216a(6) =-45056a(7) =-212992a(8) =-983040a(9) =-4456448a(10) =-19922944a(11) =-88080384a(12) =-385875968a(13) =-1677721600a(14) =-7247757312a(15) =-31138512896a(16) =-133143986176a(17) =-566935683072