a(n) = A050446(n, n) = A050447(n, n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =30a(4) =190a(5) =1547a(6) =15106a(7) =173502a(8) =2286648a(9) =34053437a(10) =565424068a(11) =10358963615a(12) =207582616995