Numbers k such that k and k+1 both have 4 divisors.

Terms

a(0) =14a(1) =21a(2) =26a(3) =33a(4) =34a(5) =38a(6) =57a(7) =85a(8) =86a(9) =93a(10) =94a(11) =118a(12) =122a(13) =133a(14) =141a(15) =142a(16) =145a(17) =158a(18) =177a(19) =201a(20) =202a(21) =205a(22) =213a(23) =214a(24) =217a(25) =218a(26) =253a(27) =298a(28) =301a(29) =302