a(n) = (2*n)!/a(n-1), with a(0)=1.

Terms

a(0) =1a(1) =2a(2) =12a(3) =60a(4) =672a(5) =5400a(6) =88704a(7) =982800a(8) =21288960a(9) =300736800a(10) =8089804800a(11) =138940401600