Leftmost column of array A275950.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =150a(5) =918a(6) =6876a(7) =63018a(8) =589518a(9) =6272712a(10) =76110150a(11) =950826294a(12) =13044895668a(13) =197045295354