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 A087604 Smallest k such that n times concatenation of k with itself followed by a 3 is a prime, or 0 if no such number exists. 7
 1, 1, 0, 1, 4, 0, 2, 1, 0, 1, 4, 0, 37, 7, 0, 17, 149, 0, 185, 7, 0, 73, 1, 0, 5, 47, 0, 38, 4, 0, 4, 133, 0, 52, 2, 0, 194, 46, 0, 37, 29, 0, 29, 25, 0, 19, 14, 0, 74, 8, 0, 19, 20, 0, 442, 83, 0, 358, 211, 0, 16, 298, 0, 260, 5, 0, 305, 71, 0, 8, 323, 0, 5, 109, 0, 8, 68, 0, 767, 367 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS Trivially a(3n) = 0. Conjecture: no other term is zero. Either a(13)=0 or a(13)>36. This sequence contains no positive multiples of 3. If a(m) is of the form bbb...b (repeated k times) then a(km) <= b. - Sam Alexander, Oct 20 2003 LINKS EXAMPLE a(5) = 4 as 444443 is a prime. but 111113,222223,333333 are not. CROSSREFS Cf. A086920, A087605, A087606, A087607, A087608, A087609, A087610. Sequence in context: A019200 A324820 A337996 * A090538 A320157 A320479 Adjacent sequences:  A087601 A087602 A087603 * A087605 A087606 A087607 KEYWORD base,nonn AUTHOR Amarnath Murthy, Sep 18 2003 EXTENSIONS More terms from Sam Alexander, Oct 20 2003 More terms from Ray G. Opao, Apr 15 2004 More terms from David Wasserman, Jun 16 2005 STATUS approved

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Last modified June 22 21:29 EDT 2021. Contains 345393 sequences. (Running on oeis4.)