a(n) = n! + (n-1)! + (n-2)!.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =32a(5) =150a(6) =864a(7) =5880a(8) =46080a(9) =408240a(10) =4032000a(11) =43908480a(12) =522547200a(13) =6745939200a(14) =93884313600