a(n) = Sum_{k=0..floor(n/3)} 2^k * binomial(2*k+1,2*n-6*k+1).

Terms

a(0) =1a(1) =0a(2) =0a(3) =6a(4) =2a(5) =0a(6) =20a(7) =40a(8) =4a(9) =56a(10) =280a(11) =168a(12) =152a(13) =1344a(14) =2016a(15) =928a(16) =5296a(17) =14784a(18) =11392a(19) =20064a(20) =82400a(21) =111744a(22) =104000a(23) =389376a(24) =828096a(25) =814720a(26) =1758848a(27) =5001856a(28) =6719616a(29) =9121792