Numbers k such that 2 and 4 occur juxtaposed in the base-10 representation of k but not of k-1.

Terms

a(0) =24a(1) =42a(2) =124a(3) =142a(4) =224a(5) =240a(6) =324a(7) =342a(8) =420a(9) =442a(10) =524a(11) =542a(12) =624a(13) =642a(14) =724a(15) =742a(16) =824a(17) =842a(18) =924a(19) =942a(20) =1024a(21) =1042a(22) =1124a(23) =1142a(24) =1224a(25) =1240a(26) =1324a(27) =1342a(28) =1420a(29) =1442