Floor(n^n/n!) - ceiling(2^n/n).

Terms

a(0) =-1a(1) =0a(2) =1a(3) =6a(4) =19a(5) =53a(6) =144a(7) =384a(8) =1010a(9) =2652a(10) =6960a(11) =18271a(12) =48007a(13) =126292a(14) =332679a(15) =877561a(16) =2318039a(17) =6131032a(18) =16236271a(19) =43047375a(20) =114256746a(21) =303570609a(22) =807327311a(23) =2148933010a(24) =5724699937a(25) =15262109996a(26) =40717942427a(27) =108704057535a(28) =290385838171a(29) =776171229484