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

Terms

a(0) =1a(1) =0a(2) =0a(3) =2a(4) =0a(5) =0a(6) =4a(7) =12a(8) =0a(9) =8a(10) =72a(11) =0a(12) =16a(13) =288a(14) =144a(15) =32a(16) =960a(17) =1440a(18) =64a(19) =2880a(20) =8640a(21) =1856a(22) =8064a(23) =40320a(24) =24448a(25) =21504a(26) =161280a(27) =194048a(28) =76032a(29) =580608