a(n) = Product_{d|n} psi(d), where psi(m) is the sum of totatives of m (A023896).

Terms

a(0) =1a(1) =1a(2) =3a(3) =4a(4) =10a(5) =18a(6) =21a(7) =64a(8) =81a(9) =200a(10) =55a(11) =1728a(12) =78a(13) =882a(14) =1800a(15) =4096a(16) =136a(17) =26244a(18) =171a(19) =64000a(20) =7938a(21) =6050a(22) =253a(23) =2654208a(24) =2500a(25) =12168a(26) =19683a(27) =592704a(28) =406a(29) =25920000