a(n) = n*(n+1)!/2 + 1.

Terms

a(0) =1a(1) =2a(2) =7a(3) =37a(4) =241a(5) =1801a(6) =15121a(7) =141121a(8) =1451521a(9) =16329601a(10) =199584001a(11) =2634508801a(12) =37362124801a(13) =566658892801