Numbers having exactly two distinct prime factors p, q with q = p+4.

Terms

a(0) =21a(1) =63a(2) =77a(3) =147a(4) =189a(5) =221a(6) =437a(7) =441a(8) =539a(9) =567a(10) =847a(11) =1029a(12) =1323a(13) =1517a(14) =1701a(15) =2021a(16) =2873a(17) =3087a(18) =3757a(19) =3773a(20) =3969a(21) =4757a(22) =5103a(23) =5929a(24) =6557a(25) =7203a(26) =8303a(27) =9261a(28) =9317a(29) =9797