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%I #8 Mar 04 2018 03:16:45
%S 3,1,1,11,113,7,23,41,37,141,733,241,3,791,781,701,239,441,2019,189,
%T 2071,401,851,463,4421,497,2267,213,1653,1683,1227,667,3261,6673,5799,
%U 3579,1907,6483,7813,2443,1923,11439,6657,7861,1847,7521,8277,8459
%N a(1) = 3, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime.
%e 3,311,311111,31111111111111 are all prime.
%e 31111111111111 = one copy of 3, two copies of 1, three copies of 1, four copies of 11.
%o (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
%Y Cf. A111471, A111472, A111474.
%K base,hard,nonn
%O 1,1
%A _Amarnath Murthy_, Aug 05 2005
%E More terms from _Max Alekseyev_, May 18 2009