a(n) = (n!/4!)*Sum(1/k!,k=1..n-4).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =5a(6) =45a(7) =350a(8) =2870a(9) =25956a(10) =259770a(11) =2857800a(12) =34294095a(13) =445823950a(14) =6241536301a(15) =93623045880