Numbers using only digits 1 and 5.

Terms

a(0) =1a(1) =5a(2) =11a(3) =15a(4) =51a(5) =55a(6) =111a(7) =115a(8) =151a(9) =155a(10) =511a(11) =515a(12) =551a(13) =555a(14) =1111a(15) =1115a(16) =1151a(17) =1155a(18) =1511a(19) =1515a(20) =1551a(21) =1555a(22) =5111a(23) =5115a(24) =5151a(25) =5155a(26) =5511a(27) =5515a(28) =5551a(29) =5555