(tau(n^4) + 3)/4, where tau = A000005.

Terms

a(0) =1a(1) =2a(2) =2a(3) =3a(4) =2a(5) =7a(6) =2a(7) =4a(8) =3a(9) =7a(10) =2a(11) =12a(12) =2a(13) =7a(14) =7a(15) =5a(16) =2a(17) =12a(18) =2a(19) =12a(20) =7a(21) =7a(22) =2a(23) =17a(24) =3a(25) =7a(26) =4a(27) =12a(28) =2a(29) =32