a(1) = 1; a(n+1) = -Sum_{d|n} d*a(d).

Terms

a(0) =1a(1) =-1a(2) =1a(3) =-4a(4) =17a(5) =-86a(6) =514a(7) =-3599a(8) =28809a(9) =-259285a(10) =2592766a(11) =-28520427a(12) =342245654a(13) =-4449193503a(14) =62288705445a(15) =-934330581764