Numbers with digits 2 and 7 only.

Terms

a(0) =2a(1) =7a(2) =22a(3) =27a(4) =72a(5) =77a(6) =222a(7) =227a(8) =272a(9) =277a(10) =722a(11) =727a(12) =772a(13) =777a(14) =2222a(15) =2227a(16) =2272a(17) =2277a(18) =2722a(19) =2727a(20) =2772a(21) =2777a(22) =7222a(23) =7227a(24) =7272a(25) =7277a(26) =7722a(27) =7727a(28) =7772a(29) =7777