A111473 a(1) = 3, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime.

3, 1, 1, 11, 113, 7, 23, 41, 37, 141, 733, 241, 3, 791, 781, 701, 239, 441, 2019, 189, 2071, 401, 851, 463, 4421, 497, 2267, 213, 1653, 1683, 1227, 667, 3261, 6673, 5799, 3579, 1907, 6483, 7813, 2443, 1923, 11439, 6657, 7861, 1847, 7521, 8277, 8459

Offset: 1

Author

Amarnath Murthy, Aug 05 2005

Keywords

• base
• hard
• nonn

Examples

			3,311,311111,31111111111111 are all prime.
31111111111111 = one copy of 3, two copies of 1, three copies of 1, four copies of 11.
		

Crossrefs

Cf. A111471, A111472, A111474.

Programs

PARI

{ x=3; for(n=2,50, k=0; until(ispseudoprime(y), k++; y=eval(concat(Str(x),concat(vector(n,i,Str(k))))); ); print1(k,", "); x=y; ) } \\ Max Alekseyev, May 18 2009

Extensions

More terms from Max Alekseyev, May 18 2009