%I A005422 M2889
%S A005422 3,11,37,101,271,37,4649,137,333667,9091,513239,9901,265371653,909091,
%T A005422 2906161,5882353,5363222357,333667,1111111111111111111,27961,10838689,
%U A005422 513239,11111111111111111111111,99990001,182521213001,1058313049
%N A005422 Largest prime factor of 10^n -1.
%D A005422 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A005422 J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, 
               Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and 
               later supplements.
%H A005422 T. D. Noe, <a href="b005422.txt">Table of n, a(n) for n=1..100</a> (derived 
               from Yousuke Koide)
%H A005422 J. Brillhart et al., <a href="http://www.ams.org/online_bks/conm22/">
               Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, 
               Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
%H A005422 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/
               cun/index.html">The Cunningham Project</a>
%H A005422 Yousuke Koide, <a href="http://www.h4.dion.ne.jp/~rep/">Factorizations 
               of Repunit Numbers</a>
%o A005422 (PARI) a(n)=local(p); if(n<1,0,p=factor(10^n-1)~[1,]; p[length(p)])
%Y A005422 Same as A003020 except for initial terms. Cf. A102380, A067063.
%Y A005422 Sequence in context: A007138 A046107 A061075 this_sequence A040017 A007615 
               A065540
%Y A005422 Adjacent sequences: A005419 A005420 A005421 this_sequence A005423 A005424 
               A005425
%K A005422 nonn
%O A005422 1,1
%A A005422 N. J. A. Sloane (njas(AT)research.att.com).