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 A046415 Repunit of length a(n) has exactly 4 prime factors (counted with multiplicity). 1
 8, 9, 10, 14, 41, 43, 49, 53, 109, 157, 167, 173, 197, 199, 223, 229, 269, 283, 307, 349 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..20. P. De Geest, Repunits prime factors Makoto Kamada, Factorizations of 11...11 (Repunit) Eric Weisstein's World of Mathematics, Repunit MATHEMATICA Select[Range[350], PrimeOmega[FromDigits[PadRight[{}, #, 1]]]==4&] (* Harvey P. Dale, Oct 27 2020 *) PROG (PARI) isok(n) = bigomega((10^n - 1)/9) == 4; \\ Michel Marcus, Apr 23 2017 CROSSREFS Cf. A000042, A001222, A002275, A004022, A004023, A046053. Sequence in context: A271211 A341044 A072381 * A358674 A358675 A091417 Adjacent sequences: A046412 A046413 A046414 * A046416 A046417 A046418 KEYWORD nonn,base,more AUTHOR Patrick De Geest, Jul 15 1998 EXTENSIONS More terms from Robert Gerbicz, Nov 22 2010 Offset corrected to 1, a(18)-a(20) added by Ray Chandler, Apr 23 2017 STATUS approved

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Last modified December 7 02:20 EST 2023. Contains 367622 sequences. (Running on oeis4.)