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%I #26 Nov 03 2019 22:34:08
%S 13,31,37,38,67,73,83,97,101,103,113,127,149,163,191,227,241,263,313,
%T 331,373,379
%N Repunit of length a(n) has exactly 3 prime factors (counted with multiplicity).
%C 467 <= a(23) <= 857. 857, 1303, 1483, 2267 are terms of this sequence. - _Chai Wah Wu_, Nov 03 2019
%H P. De Geest, <a href="http://www.worldofnumbers.com/repunits.htm">Repunits prime factors</a>
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (Repunit)</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Repunit.html">Repunit</a>
%e a(n)=13 so 1111111111111 = 53*79*265371653.
%o (PARI) is(n)=bigomega(10^n\9)==3 \\ _Charles R Greathouse IV_, Mar 11 2014
%Y Cf. A000042, A001222, A002275, A004022, A046053.
%K nonn,more,base
%O 1,1
%A _Patrick De Geest_, Jul 15 1998
%E More terms from _Robert Gerbicz_, Nov 22 2010
%E More terms from _Bo Gyu Jeong_, Jun 12 2012
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