a(n) = binomial(n, floor((n-4)/2)).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =6a(7) =7a(8) =28a(9) =36a(10) =120a(11) =165a(12) =495a(13) =715a(14) =2002a(15) =3003a(16) =8008a(17) =12376a(18) =31824a(19) =50388a(20) =125970a(21) =203490a(22) =497420a(23) =817190a(24) =1961256a(25) =3268760a(26) =7726160a(27) =13037895a(28) =30421755a(29) =51895935