a(n) = Sum_{k=0..n} binomial(3*n,4*k).

Terms

a(0) =1a(1) =1a(2) =16a(3) =136a(4) =992a(5) =8256a(6) =65536a(7) =523776a(8) =4196352a(9) =33550336a(10) =268435456a(11) =2147516416a(12) =17179738112a(13) =137439215616