a(n) = Sum_{r < n, gcd(r,n)=1} n!/r!.

Terms

a(0) =1a(1) =2a(2) =9a(3) =28a(4) =205a(5) =726a(6) =8659a(7) =47384a(8) =562545a(9) =4234330a(10) =68588311a(11) =483088332a(12) =10699776685a(13) =102434734598