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 A023729 #17 Apr 14 2025 05:33:18
%S A023729 0,1,3,4,5,6,8,9,15,16,18,19,20,21,23,24,25,26,28,29,30,31,33,34,40,
%T A023729 41,43,44,45,46,48,49,75,76,78,79,80,81,83,84,90,91,93,94,95,96,98,99,
%U A023729 100,101,103,104,105,106,108,109,115,116,118,119,120,121
%N A023729 Numbers with no 2's in their base-5 expansion.
%H A023729 Nathaniel Johnston, <a href="/A023729/b023729.txt">Table of n, a(n) for n = 1..10000</a>
%H A023729 Robert Baillie and Thomas Schmelzer, <a href="https://library.wolfram.com/infocenter/MathSource/7166/">Summing Kempner's Curious (Slowly-Convergent) Series</a>, Mathematica Notebook kempnerSums.nb, Wolfram Library Archive, 2008.
%H A023729 <a href="/index/Ar#5-automatic">Index entries for 5-automatic sequences</a>.
%F A023729 Sum_{n>=2} 1/a(n) = 6.4926328481629227744899858111920644967528391159751448517967690160220746453627777857879224296518328062481... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - _Amiram Eldar_, Apr 14 2025
%p A023729 seq(`if`(numboccur(2,convert(n,base,5))=0,n,NULL),n=0..127); # _Nathaniel Johnston_, Jun 27 2011
%t A023729 Select[ Range[ 0, 125 ], (Count[ IntegerDigits[ #, 5 ], 2 ]==0)& ]
%t A023729 Select[Range[0, 120], DigitCount[#, 5, 2] == 0 &] (* _Amiram Eldar_, Apr 14 2025 *)
%o A023729 (PARI) is(n)=while(n>2, if(n%5==2, return(0)); n\=5); 1 \\ _Charles R Greathouse IV_, Feb 12 2017
%Y A023729 Cf. A020654, A023721, A023725, A023733.
%K A023729 nonn,base,easy
%O A023729 1,3
%A A023729 _Olivier Gérard_