a(n) = binomial(2n+1,n-4).

Terms

a(0) =1a(1) =11a(2) =78a(3) =455a(4) =2380a(5) =11628a(6) =54264a(7) =245157a(8) =1081575a(9) =4686825a(10) =20030010a(11) =84672315a(12) =354817320a(13) =1476337800a(14) =6107086800a(15) =25140840660a(16) =103077446706a(17) =421171648758