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 A061978 #16 Mar 09 2020 21:16:15
%S A061978 1,3,9,21,33,57,96,864,1033,1661,6449,6624,10464,68249,81664,108981,
%T A061978 164384,167571,234311,2420409,5490464
%N A061978 Numbers n such that n divides the (left) concatenation of all numbers <= n written in base 25 (most significant digit on right).
%C A061978 This sequence differs from A029542 in that all least significant zeros are kept during concatenation.
%C A061978 No more terms < 7*10^6.
%H A061978 <a href="/index/N#concat">Index entries for related sequences</a>
%e A061978 See A061955 for example.
%t A061978 b = 25; c = {}; Select[Range[10^4], Divisible[FromDigits[c = Join[Reverse[IntegerDigits[#, b]], c], b], #] &] (* _Robert Price_, Mar 09 2020 *)
%Y A061978 Cf. A029447-A029470, A029471-A029494, A029495-A029518, A029519-A029542, A061931-A061954, A061955-A061978.
%K A061978 nonn,base,more
%O A061978 1,2
%A A061978 Larry Reeves (larryr(AT)acm.org), May 24 2001
%E A061978 Edited and updated by Larry Reeves (larryr(AT)acm.org), Apr 12 2002
%E A061978 a(20)-a(21) from _Lars Blomberg_, Jul 22 2011