Numbers of the form p*q, where p is prime and q=(p^k-1)/(p-1) is also prime for some integer k>1.

Terms

a(0) =6a(1) =14a(2) =39a(3) =62a(4) =155a(5) =254a(6) =3279a(7) =5219a(8) =16382a(9) =19607a(10) =70643a(11) =97655a(12) =208919a(13) =262142a(14) =363023a(15) =402233a(16) =712979a(17) =1040603a(18) =1048574a(19) =1508597a(20) =2265383a(21) =2391483a(22) =4685519a(23) =5207819a(24) =6728903a(25) =21243689a(26) =25239899a(27) =56328959a(28) =61035155a(29) =67977559