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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
Sequence in context: A370325 A346933 A136595 * A222581 A010139 A078075
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 March 19 01:57 EDT 2024. Contains 370952 sequences. (Running on oeis4.)