a(n) = (2^(n+1) + (-4)^n)/3.

Terms

a(0) =1a(1) =0a(2) =8a(3) =-16a(4) =96a(5) =-320a(6) =1408a(7) =-5376a(8) =22016a(9) =-87040a(10) =350208a(11) =-1396736a(12) =5595136a(13) =-22364160a(14) =89489408a(15) =-357892096a(16) =1431699456a(17) =-5726535680a(18) =22906667008a(19) =-91625619456a(20) =366504574976