a(n) = -Sum_{d|n} (-n/d)^d.

Terms

a(0) =1a(1) =1a(2) =4a(3) =-1a(4) =6a(5) =4a(6) =8a(7) =-25a(8) =37a(9) =16a(10) =12a(11) =-106a(12) =14a(13) =92a(14) =384a(15) =-561a(16) =18a(17) =-65a(18) =20a(19) =-706a(20) =2552a(21) =1948a(22) =24a(23) =-15658a(24) =3151a(25) =8048a(26) =20440a(27) =-2570a(28) =30a(29) =-33326