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

Terms

a(0) =14a(1) =41a(2) =114a(3) =140a(4) =214a(5) =241a(6) =314a(7) =341a(8) =410a(9) =441a(10) =514a(11) =541a(12) =614a(13) =641a(14) =714a(15) =741a(16) =814a(17) =841a(18) =914a(19) =941a(20) =1014a(21) =1041a(22) =1114a(23) =1140a(24) =1214a(25) =1241a(26) =1314a(27) =1341a(28) =1400a(29) =1514