Primes that contain digits 1 and 5 only.

Terms

a(0) =5a(1) =11a(2) =151a(3) =1151a(4) =1511a(5) =11551a(6) =15511a(7) =15551a(8) =51151a(9) =51511a(10) =51551a(11) =55511a(12) =115151a(13) =511111a(14) =511151a(15) =515111a(16) =1111151a(17) =1115551a(18) =1155151a(19) =1551551a(20) =1555111a(21) =5115511a(22) =5151151a(23) =5151551a(24) =5155511a(25) =5511151a(26) =5511511a(27) =5515151a(28) =5551111a(29) =15511151