Binomial coefficients C(2n, n-2).

Terms

a(0) =1a(1) =6a(2) =28a(3) =120a(4) =495a(5) =2002a(6) =8008a(7) =31824a(8) =125970a(9) =497420a(10) =1961256a(11) =7726160a(12) =30421755a(13) =119759850a(14) =471435600a(15) =1855967520a(16) =7307872110a(17) =28781143380a(18) =113380261800a(19) =446775310800