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 A093023 #15 Aug 17 2021 07:18:44 %S A093023 8,13,27,32,46,51,65,70,89,94,107,112,126,131,145,150,169,174,188,193, %T A093023 206,211,225,230,249,254,268,273,287,292,305,310,329,334,348,353,367, %U A093023 372,386,391,409,414,428,433,447,452,466,471,485,490,503,517,522,536 %N A093023 Indices of terms in A093019 with value 3. %C A093023 Integers which require a following 3 to have a valid Luhn mod 10 check digit. %H A093023 Reinhard Zumkeller, <a href="/A093023/b093023.txt">Table of n, a(n) for n = 1..10000</a> %H A093023 John Kilgo, <a href="https://web.archive.org/web/20040627030859/http://www.dotnetjohn.com/articles/articleid97.aspx">Using the Luhn Algorithm</a>, DotNetJohn.com. %H A093023 Webopedia, <a href="http://www.webopedia.com/TERM/L/Luhn_formula.html">Luhn formula</a> %H A093023 Wikipedia, <a href="http://en.wikipedia.org/wiki/Luhn_algorithm">Luhn algorithm</a> %H A093023 <a href="/index/De#decimal_expansion">Index entries for sequences related to decimal expansion of n</a> %F A093023 A093019(a(n)) = 3. - _Reinhard Zumkeller_, Nov 08 2014 %e A093023 13 is in the sequence because A093019(13)=3; 133 has a valid Luhn mod 10 check digit. %o A093023 (Haskell) %o A093023 a093023 n = a093023_list !! (n-1) %o A093023 a093023_list = filter ((== 3) . a093019) [0..] %o A093023 -- _Reinhard Zumkeller_, Nov 08 2014 %Y A093023 Cf. A093017-A093029. %K A093023 easy,nonn,base %O A093023 1,1 %A A093023 _Ray Chandler_, Apr 03 2004 %E A093023 Offset changed by _Reinhard Zumkeller_, Nov 08 2014