Numbers whose base-10 representation has the same nonzero number of 3's and 7's.

Terms

a(0) =37a(1) =73a(2) =137a(3) =173a(4) =237a(5) =273a(6) =307a(7) =317a(8) =327a(9) =347a(10) =357a(11) =367a(12) =370a(13) =371a(14) =372a(15) =374a(16) =375a(17) =376a(18) =378a(19) =379a(20) =387a(21) =397a(22) =437a(23) =473a(24) =537a(25) =573a(26) =637a(27) =673a(28) =703a(29) =713