a(n) = floor(e*(n-1)*(n-1)!).

Terms

a(0) =0a(1) =2a(2) =10a(3) =48a(4) =260a(5) =1630a(6) =11742a(7) =95900a(8) =876808a(9) =8877690a(10) =98641010a(11) =1193556232a(12) =15624736140a(13) =220048367318