Duplicate of A007340.

Terms

a(0) =1a(1) =6a(2) =140a(3) =270a(4) =672a(5) =1638a(6) =2970a(7) =6200a(8) =8190a(9) =18600a(10) =18620a(11) =27846a(12) =30240a(13) =32760a(14) =55860a(15) =105664