a(n) = 7*binomial(2n,n-3)/(n+4).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =7a(5) =35a(6) =154a(7) =637a(8) =2548a(9) =9996a(10) =38760a(11) =149226a(12) =572033a(13) =2187185a(14) =8351070a(15) =31865925a(16) =121580760a(17) =463991880a(18) =1771605360a(19) =6768687870a(20) =25880277150a(21) =99035193894a(22) =379300783092