Numbers whose base-10 representation has the same nonzero number of 2's and 4's.

Terms

a(0) =24a(1) =42a(2) =124a(3) =142a(4) =204a(5) =214a(6) =234a(7) =240a(8) =241a(9) =243a(10) =245a(11) =246a(12) =247a(13) =248a(14) =249a(15) =254a(16) =264a(17) =274a(18) =284a(19) =294a(20) =324a(21) =342a(22) =402a(23) =412a(24) =420a(25) =421a(26) =423a(27) =425a(28) =426a(29) =427