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 A086920 Smallest k such that n times concatenation of k with itself followed by a 1 is a prime, or 0 if no such number exists. 7
 1, 3, 2, 3, 3, 3, 3, 30, 6, 4, 5, 5, 25, 42, 17, 19, 2, 1, 7, 6, 6, 1, 50, 29, 138, 153, 4, 45, 54, 7, 15, 9, 78, 147, 95, 58, 102, 18, 3, 115, 54, 6, 46, 9, 24, 64, 183, 120, 3, 33, 112, 46, 105, 4, 279, 122, 68, 75, 3, 22, 294, 56, 92, 76, 6, 19, 94, 71, 12, 75, 30, 16, 78, 320, 33 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Conjecture: no term is zero. LINKS EXAMPLE a(3) = 2 as 2221 is a prime. a(4) = 3 as 33331 is a prime but 11111 and 22221 are not. a(8) = 30 and the prime arising is 30303030303030301. CROSSREFS Cf. A087604, A087605, A087606, A087607, A087608, A087609. Cf. A086923. Cf. A086766. Sequence in context: A065801 A265705 A205237 * A182021 A117451 A130970 Adjacent sequences:  A086917 A086918 A086919 * A086921 A086922 A086923 KEYWORD base,nonn AUTHOR Amarnath Murthy, Sep 18 2003 EXTENSIONS More terms from Ray G. Opao, Apr 15 2004 More terms from David Wasserman, Apr 12 2005 STATUS approved

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Last modified October 1 11:59 EDT 2020. Contains 337443 sequences. (Running on oeis4.)