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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =1a(5) =6a(6) =1a(7) =39a(8) =4a(9) =8a(10) =1a(11) =330a(12) =1a(13) =10a(14) =9a(15) =12495a(16) =1a(17) =1446a(18) =1a(19) =1620a(20) =11a(21) =14a(22) =1a(23) =1792050a(24) =6a(25) =16a(26) =580a(27) =10158a(28) =1a(29) =53002