a(1) = 1; a(n) = -Sum_{d|n, d<n} prime(n/d) * a(d).

Terms

a(0) =1a(1) =-3a(2) =-5a(3) =2a(4) =-11a(5) =17a(6) =-17a(7) =-4a(8) =2a(9) =37a(10) =-31a(11) =-24a(12) =-41a(13) =59a(14) =63a(15) =2a(16) =-59a(17) =-18a(18) =-67a(19) =-40a(20) =97a(21) =107a(22) =-83a(23) =64a(24) =24a(25) =145a(26) =2a(27) =-70a(28) =-109a(29) =-245