a(n) = Sum_{k=0..floor(n/3)} (k+1) * 2^k * 3^(n-3*k) * binomial(k,3*(n-3*k)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =4a(4) =0a(5) =0a(6) =12a(7) =0a(8) =0a(9) =32a(10) =96a(11) =0a(12) =80a(13) =960a(14) =0a(15) =192a(16) =5760a(17) =0a(18) =448a(19) =26880a(20) =4032a(21) =1024a(22) =107520a(23) =64512a(24) =2304a(25) =387072a(26) =580608a(27) =5120a(28) =1290240a(29) =3870720