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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
OFFSET
1,1
EXAMPLE
7,733,733111,... are all prime.
733111 = one copy of 7, two copies of 3, three copies of 1.
CROSSREFS
KEYWORD
base,hard,nonn
AUTHOR
Amarnath Murthy, Aug 05 2005
EXTENSIONS
Extended by Max Alekseyev, May 19 2009
STATUS
approved