a(n) = lcm(n^2, n!) / lcm(n^2, swinging_factorial(n)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =4a(6) =4a(7) =36a(8) =18a(9) =64a(10) =576a(11) =14400a(12) =43200a(13) =518400a(14) =518400a(15) =5080320a(16) =12700800a(17) =1625702400a(18) =1625702400a(19) =131681894400a(20) =131681894400a(21) =627056640000