a(n) = (n!)^2*Sum_{k=1..n} 1/k!.

A061573

a(n) = (n!)^2*Sum_{k=1..n} 1/k!.

Terms

    a(0) =1a(1) =6a(2) =60a(3) =984a(4) =24720a(5) =890640a(6) =43646400a(7) =2793409920a(8) =226266566400

External references