Numbers whose base-10 representation has the same nonzero number of 1's and 5's.

Terms

a(0) =15a(1) =51a(2) =105a(3) =125a(4) =135a(5) =145a(6) =150a(7) =152a(8) =153a(9) =154a(10) =156a(11) =157a(12) =158a(13) =159a(14) =165a(15) =175a(16) =185a(17) =195a(18) =215a(19) =251a(20) =315a(21) =351a(22) =415a(23) =451a(24) =501a(25) =510a(26) =512a(27) =513a(28) =514a(29) =516