a(n) = (n!/5!)*Sum(1/k!,k=1..n-5).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =6a(7) =63a(8) =560a(9) =5166a(10) =51912a(11) =571494a(12) =6858720a(13) =89164647a(14) =1248307060a(15) =18724608903a(16) =299593746816