%I #15 Aug 17 2021 06:27:23
%S 9,14,28,33,47,52,66,71,85,90,108,113,127,132,146,151,165,170,189,194,
%T 207,212,226,231,245,250,269,274,288,293,306,311,325,330,349,354,368,
%U 373,387,392,405,410,429,434,448,453,467,472,486,491,504,518,523,537
%N Indices of terms in A093019 with value 1.
%C Integers which require a following 1 to have a valid Luhn mod 10 check digit.
%H Reinhard Zumkeller, <a href="/A093021/b093021.txt">Table of n, a(n) for n = 1..10000</a>
%H 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 Webopedia, <a href="http://www.webopedia.com/TERM/L/Luhn_formula.html">Luhn formula</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Luhn_algorithm">Luhn algorithm</a>
%H <a href="/index/De#decimal_expansion">Index entries for sequences related to decimal expansion of n</a>
%F A093019(a(n)) = 1. - _Reinhard Zumkeller_, Nov 08 2014
%e 14 is in the sequence because A093019(14)=1; 141 has a valid Luhn mod 10 check digit.
%o (Haskell)
%o a093021 n = a093021_list !! (n-1)
%o a093021_list = filter ((== 1) . a093019) [0..]
%o -- _Reinhard Zumkeller_, Nov 08 2014
%Y Cf. A093017-A093029.
%K easy,nonn,base
%O 1,1
%A _Ray Chandler_, Apr 03 2004
%E Offset changed by _Reinhard Zumkeller_, Nov 08 2014