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

Terms

a(0) =0a(1) =2a(2) =6a(3) =12a(4) =24a(5) =40a(6) =72a(7) =112a(8) =192a(9) =288a(10) =480a(11) =704a(12) =1152a(13) =1664a(14) =2688a(15) =3840a(16) =6144a(17) =8704a(18) =13824a(19) =19456a(20) =30720a(21) =43008a(22) =67584a(23) =94208a(24) =147456a(25) =204800a(26) =319488a(27) =442368a(28) =688128a(29) =950272