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 A111475 a(1) = 7, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime. 5
 7, 3, 1, 1, 1, 1, 129, 123, 97, 559, 781, 459, 253, 183, 413, 417, 657, 77, 437, 1439, 667, 1281, 3379, 979, 2763, 1953, 103, 10083, 5103, 291, 1311, 2199, 1159, 501, 5931, 483, 6171, 16301, 1781, 1229, 9519, 607, 5113, 2641, 1441, 8511, 9023, 363, 4001, 15261 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE 7,733,733111,... are all prime. 733111 = one copy of 7, two copies of 3, three copies of 1. CROSSREFS Cf. A111471, A111472, A111473, A111474, A111476. Sequence in context: A334060 A083803 A136595 * A222581 A010139 A078075 Adjacent sequences:  A111472 A111473 A111474 * A111476 A111477 A111478 KEYWORD base,hard,nonn AUTHOR Amarnath Murthy, Aug 05 2005 EXTENSIONS Extended by Max Alekseyev, May 19 2009 STATUS approved

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Last modified May 6 15:17 EDT 2021. Contains 343586 sequences. (Running on oeis4.)