a(n) = Product_{k=0..n-1} (3*n-4*k).

Terms

a(0) =1a(1) =3a(2) =12a(3) =45a(4) =0a(5) =-3465a(6) =-60480a(7) =-626535a(8) =0a(9) =204417675a(10) =6227020800a(11) =104928949125a(12) =0a(16) =0a(20) =0