Numbers k with digits 5 and 7 only.

Terms

a(0) =5a(1) =7a(2) =55a(3) =57a(4) =75a(5) =77a(6) =555a(7) =557a(8) =575a(9) =577a(10) =755a(11) =757a(12) =775a(13) =777a(14) =5555a(15) =5557a(16) =5575a(17) =5577a(18) =5755a(19) =5757a(20) =5775a(21) =5777a(22) =7555a(23) =7557a(24) =7575a(25) =7577a(26) =7755a(27) =7757a(28) =7775a(29) =7777