a(n) = Sum_{d|n} phi(n/d) * (-2)^(d-1).

Terms

a(0) =1a(1) =-1a(2) =6a(3) =-8a(4) =20a(5) =-30a(6) =70a(7) =-136a(8) =270a(9) =-500a(10) =1034a(11) =-2088a(12) =4108a(13) =-8134a(14) =16440a(15) =-32912a(16) =65552a(17) =-130878a(18) =262162a(19) =-524800a(20) =1048740a(21) =-2096138a(22) =4194326a(23) =-8390976a(24) =16777300a(25) =-33550348a(26) =67109418a(27) =-134225840a(28) =268435484a(29) =-536855640