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 A029497 #22 Jul 29 2021 01:02:00
%S A029497 1,2,3,11,207,1239,7947,9233,49883,118669,315629,2640670
%N A029497 Numbers k such that k divides the (right) concatenation of all numbers <= k written in base 4 (most significant digit on right).
%C A029497 This sequence differs from A061933 in that all least significant zeros are kept during concatenation.
%C A029497 a(13) exceeds 10000000. - _Sean A. Irvine_, Sep 01 2009
%H A029497 <a href="/index/N#concat">Index entries for related sequences</a>
%e A029497 See A029495 for example.
%t A029497 b = 4; c = {}; Select[Range[10^4], Divisible[FromDigits[c = Join[c, Reverse[IntegerDigits[#, b]]], b], #] &] (* _Robert Price_, Mar 12 2020 *)
%Y A029497 Cf. A029447-A029470, A029471-A029494, A029495-A029518, A029519-A029542, A061931-A061954, A061955-A061978.
%K A029497 nonn,base,more
%O A029497 1,2
%A A029497 _Olivier Gérard_
%E A029497 Edited and updated by Larry Reeves (larryr(AT)acm.org), Apr 12 2002
%E A029497 Additional comments and more terms from Larry Reeves (larryr(AT)acm.org), May 25 2001
%E A029497 a(12) from _Sean A. Irvine_, Sep 01 2009