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

Terms

a(0) =1a(1) =0a(2) =0a(3) =2a(4) =0a(5) =0a(6) =4a(7) =0a(8) =0a(9) =8a(10) =24a(11) =0a(12) =16a(13) =192a(14) =0a(15) =32a(16) =960a(17) =0a(18) =64a(19) =3840a(20) =576a(21) =128a(22) =13440a(23) =8064a(24) =256a(25) =43008a(26) =64512a(27) =512a(28) =129024a(29) =387072