This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A309390 #20 Aug 07 2019 14:23:05 %S A309390 10,100,101,102,12,21,112,120,103,30,130,104,14,41,114,124,121,122, %T A309390 123,23,32,132,125,25,52,152,126,16,61,106,105,50,150,107,70,170,108, %U A309390 18,81,118,128,127,27,72,172,129,29,92,192,142,134,34,43,143,140,109,90,190,110,160,116 %N A309390 Set a(1)=10. Thereafter a(n) is the smallest positive number not yet in the sequence that contains exactly one even digit and one odd digit from a(n-1). %C A309390 Numbers such as 3, 8, 20, 31, and 42 are not in the sequence since by definition all terms must contain both odd and even digits. %e A309390 a(2)=100 since it is the smallest number not yet in the sequence that contains an even digit (0) and an odd digit (1) from a(1)=10. %e A309390 a(7)=112 since it is the smallest number not yet in the sequence that contains an even digit (2) and an odd digit (1) from a(6)=21. %e A309390 a(27)=126 is not 105 since 105 would contain two odd digits (1 and 5) from a(26)=152. %Y A309390 Cf. A318700 (positive numbers that contain both odd and even digits). %K A309390 nonn,base %O A309390 1,1 %A A309390 _Enrique Navarrete_, Jul 27 2019