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 A061973 #18 Dec 05 2020 11:16:42
%S A061973 1,19,57,741,1653,44707,1434853,4392463
%N A061973 Numbers n such that n divides the (left) concatenation of all numbers <= n written in base 20 (most significant digit on right).
%C A061973 This sequence differs from A029537 in that all least significant zeros are kept during concatenation.
%C A061973 No more terms < 8*10^6. - _Lars Blomberg_, Jul 29 2011
%H A061973 <a href="/index/N#concat">Index entries for related sequences</a>
%e A061973 See A061955 for example.
%t A061973 b = 20; c = {}; Select[Range[10^4], Divisible[FromDigits[c = Join[Reverse[IntegerDigits[#, b]], c], b], #] &] (* _Robert Price_, Mar 09 2020 *)
%o A061973 (PARI) lista(nn, m=20) = my(c, t); for(k=1, nn, t+=m^c*fromdigits(Vecrev(digits(k, m)), m); c+=logint(m*k, m); if(t%k==0, print1(k, ", "))); \\ _Jinyuan Wang_, Dec 05 2020
%Y A061973 Cf. A029447-A029470, A029471-A029494, A029495-A029518, A029519-A029542, A061931-A061954, A061955-A061978.
%K A061973 nonn,base,more
%O A061973 1,2
%A A061973 Larry Reeves (larryr(AT)acm.org), May 24 2001
%E A061973 Edited and updated by Larry Reeves (larryr(AT)acm.org), Apr 12 2002
%E A061973 a(7)-a(8) from _Lars Blomberg_, Jul 29 2011