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 A093027 #16 Aug 17 2021 06:25:34 %S A093027 6,11,25,30,49,54,68,73,87,92,105,110,129,134,148,153,167,172,186,191, %T A093027 209,214,228,233,247,252,266,271,285,290,308,313,327,332,346,351,365, %U A093027 370,389,394,407,412,426,431,445,450,469,474,488,493,501,515,520,539 %N A093027 Indices of terms in A093019 with value 7. %C A093027 Integers which require a following 7 to have a valid Luhn mod 10 check digit. %H A093027 Reinhard Zumkeller, <a href="/A093027/b093027.txt">Table of n, a(n) for n = 1..10000</a> %H A093027 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 A093027 Webopedia, <a href="http://www.webopedia.com/TERM/L/Luhn_formula.html">Luhn formula</a> %H A093027 Wikipedia, <a href="http://en.wikipedia.org/wiki/Luhn_algorithm">Luhn algorithm</a> %H A093027 <a href="/index/De#decimal_expansion">Index entries for sequences related to decimal expansion of n</a> %F A093027 A093019(a(n)) = 7. - _Reinhard Zumkeller_, Nov 08 2014 %e A093027 11 is in the sequence because A093019(11)=7; 117 has a valid Luhn mod 10 check digit. %o A093027 (Haskell) %o A093027 a093027 n = a093027_list !! (n-1) %o A093027 a093027_list = filter ((== 7) . a093019) [0..] %o A093027 -- _Reinhard Zumkeller_, Nov 08 2014 %Y A093027 Cf. A093017-A093029. %K A093027 easy,nonn,base %O A093027 1,1 %A A093027 _Ray Chandler_, Apr 03 2004 %E A093027 Offset changed by _Reinhard Zumkeller_, Nov 08 2014