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%I #41 Jul 08 2022 08:19:33
%S 11,3,11,41,3,239,11,3,11,21649,3,53,11,3,11,2071723,3,
%T 1111111111111111111,11,3,11,11111111111111111111111,3,41,11,3,11,
%U 3191,3,2791,11,3,11,41,3,2028119,11,3,11,83,3,173,11,3,11,35121409,3,239
%N Smallest prime factor of repunit(n) = (10^n-1)/9 (A002275).
%C a(n) = A003020(n) = R_(n) iff n is a term of A004023. - _Bernard Schott_, May 22 2022
%D David Wells, The Penguin Dictionary of Curious and Interesting Numbers.
%H Ray Chandler, <a href="/A067063/b067063.txt">Table of n, a(n) for n = 2..508</a> (first 499 terms from T. D. Noe - corrected 7 terms)
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit">Factorizations of 11...11 (Repunit)</a>.
%H Yousuke Koide, <a href="http://www.h4.dion.ne.jp/~rep/">Factorizations of Repunit Numbers</a>
%H Amarnath Murthy, <a href="http://fs.gallup.unm.edu/SNJ11.pdf">On the divisors of Smarandache Unary Sequence</a>, Smarandache Notions Journal, Vol. 11, No. 1-2-3, Spring 2000, page 184.
%H Samuel S. Wagstaff, <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">the Cunningham Project</a>
%F a(3n) = 3, a(6n-4) = a(6n-2) = 11, a(30n-25) = a(30n-5) = 41, ... - _M. F. Hasler_, Nov 21 2006
%F a(n) = A020639(A002275(n)). - _Ray Chandler_, Apr 22 2017
%p 'min(op(numtheory[factorset]((10^k-1)/9)))'$k=2..50; # _M. F. Hasler_, Nov 21 2006
%t a = {}; Do[a = Append[a, FactorInteger[(10^n - 1)/9][[1, 1]]], {n, 2, 111} ]; a
%t Table[FactorInteger[FromDigits[PadRight[{},n,1]]][[1,1]],{n,2,50}] (* _Harvey P. Dale_, Dec 10 2013 *)
%Y Cf. A002275, A004023, A020639, A102380.
%Y Largest factor: A003020.
%K nonn
%O 2,1
%A _Amarnath Murthy_, Jan 03 2002
%E More terms from _Robert G. Wilson v_, Jan 04 2002
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