a(n) = (n!/3!)*Sum(1/k!,k=1..n-3).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =4a(5) =30a(6) =200a(7) =1435a(8) =11536a(9) =103908a(10) =1039200a(11) =11431365a(12) =137176600a(13) =1783296086a(14) =24966145568a(15) =374492183975