a(n) = n!/6!.

Terms

a(0) =1a(1) =7a(2) =56a(3) =504a(4) =5040a(5) =55440a(6) =665280a(7) =8648640a(8) =121080960a(9) =1816214400a(10) =29059430400a(11) =494010316800