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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

%I

%S 7,3,1,1,1,1,129,123,97,559,781,459,253,183,413,417,657,77,437,1439,

%T 667,1281,3379,979,2763,1953,103,10083,5103,291,1311,2199,1159,501,

%U 5931,483,6171,16301,1781,1229,9519,607,5113,2641,1441,8511,9023,363,4001,15261

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

%e 7,733,733111,... are all prime.

%e 733111 = one copy of 7, two copies of 3, three copies of 1.

%Y Cf. A111471, A111472, A111473, A111474, A111476.

%K base,hard,nonn

%O 1,1

%A _Amarnath Murthy_, Aug 05 2005

%E Extended by _Max Alekseyev_, May 19 2009

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Last modified June 24 22:23 EDT 2021. Contains 345445 sequences. (Running on oeis4.)