a(n) = (n!/24) * Sum_{k=0..n-4} 1/k!.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =10a(6) =75a(7) =560a(8) =4550a(9) =41076a(10) =410970a(11) =4521000a(12) =54252495a(13) =705283150a(14) =9873965101a(15) =148109477880