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%I #13 Nov 18 2018 00:29:58
%S 3,23,7,720901,956759,41,4769888443
%N a(n) is the beginning of the first set of n consecutive primes such that the concatenation of n with each of these primes is also prime.
%C a(8) > 10^11, a(9) = 11408039. - _Hans Havermann_, Sep 16 2005
%e a(3) = 7 because 7, 11 and 13 are 3 consecutive primes and 37, 311 and 313 are all prime.
%t <<NumberTheory`; Do[s = 0; l = {}; While[Length[l] < n, s++; l = List[Prime[s]]; k = 1; While[k < n, p = l[[k]]; AppendTo[l, NextPrime[p]]; k++ ]; l = ToString /@ l; l = Map[ToString[n] <> #&, l]; l = ToExpression /@ l; l = Select[l, PrimeQ]]; Print[Prime[s]], {n, 1, 30}]; (* _Ryan Propper_, Aug 14 2005 *)
%K base,hard,nonn
%O 1,1
%A _Amarnath Murthy_, Oct 15 2003
%E Corrected, extended and edited by _Ryan Propper_ and _David Wasserman_, Aug 14 2005
%E a(7) from _Hans Havermann_, Sep 16 2005