a(1) = 1; a(n) = phi(n) - phi(n-1)* a(n-1) if n > 1.

Terms

a(0) =1a(1) =0a(2) =2a(3) =-2a(4) =8a(5) =-30a(6) =66a(7) =-392a(8) =1574a(9) =-9440a(10) =37770a(11) =-377696a(12) =1510796a(13) =-18129546a(14) =108777284a(15) =-870218264a(16) =6961746128a(17) =-111387938042a(18) =668327628270