a(n) = Product_{p|n, p prime} (1 - p^p).

Terms

a(0) =1a(1) =-3a(2) =-26a(3) =-3a(4) =-3124a(5) =78a(6) =-823542a(7) =-3a(8) =-26a(9) =9372a(10) =-285311670610a(11) =78a(13) =2470626a(14) =81224a(15) =-3a(17) =78a(19) =9372a(20) =21412092a(21) =855935011830a(23) =78a(24) =-3124a(26) =-26a(27) =2470626