A111475 a(1) = 7, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime.

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

Author

Amarnath Murthy, Aug 05 2005

Keywords

• base
• hard
• nonn

Examples

			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.

Extensions

Extended by Max Alekseyev, May 19 2009