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 A102782 Repunit semiprimes. 5
 111, 1111, 11111, 1111111, 11111111111, 11111111111111111, 11111111111111111111111111111111111111111111111, 11111111111111111111111111111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS FORMULA a(n) = A000042(A046413(n-1)). - Ray Chandler, Sep 06 2005 EXAMPLE a(2)=1111 because 1111=11*101, so 1111 is semiprime as well as a repunit number. MATHEMATICA Select[Table[FromDigits[PadRight[{}, n, 1]], {n, 60}], PrimeOmega[#]==2&] (* Harvey P. Dale, Aug 28 2013 *) CROSSREFS Cf. A046413 the repunit of length n has exactly 2 prime factors. Sequence in context: A290619 A290627 A199979 * A302475 A303256 A137465 Adjacent sequences:  A102779 A102780 A102781 * A102783 A102784 A102785 KEYWORD base,nonn AUTHOR Shyam Sunder Gupta, Feb 11 2005 STATUS approved

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Last modified February 24 09:40 EST 2020. Contains 332209 sequences. (Running on oeis4.)