a(n) = binomial(n, floor((n-3)/2)).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =5a(6) =6a(7) =21a(8) =28a(9) =84a(10) =120a(11) =330a(12) =495a(13) =1287a(14) =2002a(15) =5005a(16) =8008a(17) =19448a(18) =31824a(19) =75582a(20) =125970a(21) =293930a(22) =497420a(23) =1144066a(24) =1961256a(25) =4457400a(26) =7726160a(27) =17383860a(28) =30421755a(29) =67863915