A111471 a(1) = 1; for n>1, a(n) = least k such that concatenation of n copies of k with all previous concatenations gives a prime.

1, 9, 7, 3, 29, 19, 21, 121, 7, 211, 207, 11, 221, 347, 99, 123, 303, 189, 1131, 1179, 2069, 3437, 2211, 211, 3169, 1551, 3493, 7433, 6939, 1053, 1537, 9417, 4491, 1257, 19693, 9, 1653, 3329, 317, 8667, 799, 1053, 5617, 6049, 1721, 24871, 2751, 737, 3303, 29079

Offset: 1

Author

Amarnath Murthy, Aug 05 2005

Keywords

• base
• nonn

Examples

			199, 199777, 1997773333, 19977733332929292929 are all primes.
		

Crossrefs

Cf. A111472.

Extensions

More terms from Donovan Johnson, Feb 26 2008