Numbers which have only digits 7 and 8 in base 10.

Terms

a(0) =7a(1) =8a(2) =77a(3) =78a(4) =87a(5) =88a(6) =777a(7) =778a(8) =787a(9) =788a(10) =877a(11) =878a(12) =887a(13) =888a(14) =7777a(15) =7778a(16) =7787a(17) =7788a(18) =7877a(19) =7878a(20) =7887a(21) =7888a(22) =8777a(23) =8778a(24) =8787a(25) =8788a(26) =8877a(27) =8878a(28) =8887a(29) =8888