Numbers whose base-10 representation has the same nonzero number of 1's and 7's.

Terms

a(0) =17a(1) =71a(2) =107a(3) =127a(4) =137a(5) =147a(6) =157a(7) =167a(8) =170a(9) =172a(10) =173a(11) =174a(12) =175a(13) =176a(14) =178a(15) =179a(16) =187a(17) =197a(18) =217a(19) =271a(20) =317a(21) =371a(22) =417a(23) =471a(24) =517a(25) =571a(26) =617a(27) =671a(28) =701a(29) =710