Numbers which have only digits 6 and 7 in base 10.

Terms

a(0) =6a(1) =7a(2) =66a(3) =67a(4) =76a(5) =77a(6) =666a(7) =667a(8) =676a(9) =677a(10) =766a(11) =767a(12) =776a(13) =777a(14) =6666a(15) =6667a(16) =6676a(17) =6677a(18) =6766a(19) =6767a(20) =6776a(21) =6777a(22) =7666a(23) =7667a(24) =7676a(25) =7677a(26) =7766a(27) =7767a(28) =7776a(29) =7777