Sum_{d divides n} (-d)^d.

Terms

a(0) =-1a(1) =3a(2) =-28a(3) =259a(4) =-3126a(5) =46632a(6) =-823544a(7) =16777475a(8) =-387420517a(9) =9999996878a(10) =-285311670612