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 A029520 #40 Jan 13 2025 13:19:10
%S A029520 1,4,5,7,19,443,19952,81544,919648,1186844
%N A029520 Numbers k such that k divides the (left) concatenation of all numbers <= k written in base 3 (most significant digit on right and removing all least significant zeros before concatenation).
%C A029520 This sequence differs from A061956 in that all least significant zeros are removed before concatenation.
%C A029520 No more terms < 10^7. [_Lars Blomberg_, Sep 02 2011]
%H A029520 <a href="/index/N#concat">Index entries for related sequences</a>
%e A029520 See A029519 for example.
%t A029520 b = 3; c = {}; Select[Range[10^4], Divisible[FromDigits[c = Join[IntegerDigits[IntegerReverse[#, b], b], c], b], #] &] (* _Robert Price_, Mar 13 2020 *)
%o A029520 (J) ab=. #.^:_1
%o A029520 mkcat=. [ ab&.> [ #.&.> [ |.@:ab&.> [: |. [: >: [: i. ]
%o A029520 seq=. ] +. [ #. [: ; mkcat
%o A029520 3 (] #~ ] = seq"0) >: i.500x NB. _Stephen Makdisi_, May 03 2018
%Y A029520 Cf. A029447-A029470, A029471-A029494, A029495-A029518, A029519-A029542, A061931-A061954, A061955-A061978.
%K A029520 nonn,base,more
%O A029520 1,2
%A A029520 _Olivier Gérard_
%E A029520 Edited and updated by Larry Reeves (larryr(AT)acm.org), Apr 12 2002
%E A029520 Additional comments and more terms from Larry Reeves (larryr(AT)acm.org), Jun 04 2001
%E A029520 a(9)-a(10) from _Lars Blomberg_, Sep 02 2011