a(n) = Sum_{d|n} (-n)^(d-1).

Terms

a(0) =1a(1) =-1a(2) =10a(3) =-67a(4) =626a(5) =-7745a(6) =117650a(7) =-2097671a(8) =43046803a(9) =-999990009a(10) =25937424602a(11) =-743008621115