Numbers n such that d(d(n)) is an odd prime, where d(k) is the number of divisors of k.

Terms

a(0) =6a(1) =8a(2) =10a(3) =14a(4) =15a(5) =21a(6) =22a(7) =26a(8) =27a(9) =33a(10) =34a(11) =35a(12) =36a(13) =38a(14) =39a(15) =46a(16) =51a(17) =55a(18) =57a(19) =58a(20) =62a(21) =65a(22) =69a(23) =74a(24) =77a(25) =82a(26) =85a(27) =86a(28) =87a(29) =91