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 A061955 #24 Mar 07 2020 20:20:10
%S A061955 1,3,7,29,375,545,971,1643,37801,435805,554423,565947,645915,733533,
%T A061955 871927,9703985
%N A061955 Numbers n such that n divides the (left) concatenation of all numbers <= n written in base 2 (most significant digit on right).
%C A061955 This sequence differs from A029519 in that all least significant zeros are kept during concatenation.
%C A061955 No more terms < 10^7. - _Lars Blomberg_, Aug 31 2011
%H A061955 <a href="/index/N#concat">Index entries for related sequences</a>
%e A061955 7654321 -> (111)(011)(101)(001)(11)(01)(1) base 2 ->11101110100111011 base 2 = 122171 and 7 divides 122171.
%t A061955 b = 2; c = {}; Select[Range[10^4], Divisible[FromDigits[c = Join[Reverse[IntegerDigits[#, b]], c], b], #] &] (* _Robert Price_, Mar 07 2020 *)
%o A061955 (PARI) is(n) = my(t=[]); for(k=1, n, t=concat(Vecrev(binary(k)), t)); if(Mod(subst(Pol(t), x, 2), n)==0, return(1), return(0)) \\ _Felix Fröhlich_, Jul 06 2017
%Y A061955 Cf. A029447-A029470, A029471-A029494, A029495-A029518, A029519-A029542, A061931-A061954, A061955-A061978.
%K A061955 nonn,base,more
%O A061955 1,2
%A A061955 Larry Reeves (larryr(AT)acm.org), May 24 2001
%E A061955 Edited and updated by Larry Reeves (larryr(AT)acm.org), Apr 12 2002; Aug 25 2002
%E A061955 a(13)-a(16) from _Lars Blomberg_, Aug 31 2011