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 A141742 #5 Mar 17 2025 14:33:41 %S A141742 3,6,7,12,13,14,15,24,25,26,27,28,29,30 %N A141742 Starting from the 1 in the first line of triangle A141728 choose one of the three digits below it. Repeat down to the other rows. Sequence gives the numbers in base 10 expressed by the collected digits that cannot be reached following any possible path. %e A141742 Below the 1 in the first row we have three 0. Therefore we cannot have "11", 3 in base 10. %Y A141742 Cf. A004755, A141727 - A141741, A141743 - A141746. %K A141742 easy,nonn %O A141742 0,1 %A A141742 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jul 07 2008