a(n) = T(n,n-3), array T as in A047130.

Terms

a(0) =1a(1) =4a(2) =14a(3) =48a(4) =151a(5) =496a(6) =1679a(7) =4892a(8) =16099a(9) =55566a(10) =126070a(11) =437604a(12) =1610354a(13) =10586223a(14) =37753710a(15) =142615460a(16) =545804530a(17) =2501659594a(18) =9822392246a(19) =38387432220a(20) =149904480000a(21) =622664257407