a(n) = n! * Sum_{d|n} mu(d) / d!.

Terms

a(0) =1a(1) =1a(2) =5a(3) =12a(4) =119a(5) =241a(6) =5039a(7) =20160a(8) =302400a(9) =1784161a(10) =39916799a(11) =160332480a(12) =6227020799a(13) =43571848321