Numbers k such that tau(tau(k)) = rad(k).

Terms

a(0) =1a(1) =2a(2) =4a(3) =16a(4) =27a(5) =64a(6) =72a(7) =96a(8) =108a(9) =288a(10) =432a(11) =486a(12) =648a(13) =768a(14) =972a(15) =1024a(16) =1536a(17) =1728a(18) =3456a(19) =4096a(20) =5832a(21) =6561a(22) =13122a(23) =17496a(24) =20736a(25) =24576a(26) =27648a(27) =39366a(28) =41472a(29) =65536