Least number k such that tau(tau(k)) = n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =12a(4) =120a(5) =60a(6) =7560a(7) =360a(8) =1260a(9) =2520a(10) =294053760a(11) =5040a(12) =128501493120a(13) =332640a(14) =110880a(15) =55440a(17) =277200a(19) =720720a(20) =21621600a(21) =27935107200a(23) =3603600a(24) =857656800a(26) =227026800a(27) =183783600