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%I #23 Oct 27 2020 15:24:41
%S 8,9,10,14,41,43,49,53,109,157,167,173,197,199,223,229,269,283,307,349
%N Repunit of length a(n) has exactly 4 prime factors (counted with multiplicity).
%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>
%t Select[Range[350],PrimeOmega[FromDigits[PadRight[{},#,1]]]==4&] (* _Harvey P. Dale_, Oct 27 2020 *)
%o (PARI) isok(n) = bigomega((10^n - 1)/9) == 4; \\ _Michel Marcus_, Apr 23 2017
%Y Cf. A000042, A001222, A002275, A004022, A004023, A046053.
%K nonn,base,more
%O 1,1
%A _Patrick De Geest_, Jul 15 1998
%E More terms from _Robert Gerbicz_, Nov 22 2010
%E Offset corrected to 1, a(18)-a(20) added by _Ray Chandler_, Apr 23 2017
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