a(n) = Sum_{k=0..floor(n/3)} 2^k * binomial(2*k,2*n-6*k).

Terms

a(0) =1a(1) =0a(2) =0a(3) =2a(4) =2a(5) =0a(6) =4a(7) =24a(8) =4a(9) =8a(10) =120a(11) =120a(12) =24a(13) =448a(14) =1120a(15) =480a(16) =1456a(17) =6720a(18) =6784a(19) =5664a(20) =31712a(21) =59264a(22) =43328a(23) =132352a(24) =384704a(25) =415104a(26) =594048a(27) =2062208a(28) =3373184a(29) =3616768