Numbers using only digits 1 and 7.

Terms

a(0) =1a(1) =7a(2) =11a(3) =17a(4) =71a(5) =77a(6) =111a(7) =117a(8) =171a(9) =177a(10) =711a(11) =717a(12) =771a(13) =777a(14) =1111a(15) =1117a(16) =1171a(17) =1177a(18) =1711a(19) =1717a(20) =1771a(21) =1777a(22) =7111a(23) =7117a(24) =7171a(25) =7177a(26) =7711a(27) =7717a(28) =7771a(29) =7777