a(n) = tau(tau(n)).

Terms

a(0) =1a(1) =2a(2) =2a(3) =2a(4) =2a(5) =3a(6) =2a(7) =3a(8) =2a(9) =3a(10) =2a(11) =4a(12) =2a(13) =3a(14) =3a(15) =2a(16) =2a(17) =4a(18) =2a(19) =4a(20) =3a(21) =3a(22) =2a(23) =4a(24) =2a(25) =3a(26) =3a(27) =4a(28) =2a(29) =4