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%I #8 Nov 18 2018 00:46:05
%S 1,2,1,7,2,2,24,8,1,103,1,12,43,94,21,1,11,12,4,23,27,4,89,20,42,1,43,
%T 6,41,44,190,22,12,139,41,114,16,3,26,171,32,220,78,86,135,117,21,44,
%U 49,143,248,175,9,76,6,66,426,46,237,252,9,62,319,88,150,123,61,122,300,15
%N Smallest k such that the concatenation r*k for r = 1 to n followed by a 1 is a prime.
%e a(4) = 7 and the prime is 71421281 = A089328(4).
%t Do[s = ""; k = 0; While[ !PrimeQ[ToExpression[s]], s = ""; k++; For[r = 1, r <= n, r++, s = s <> ToString[r*k]]; s = s <> "1"]; Print[k], {n, 1, 50}] (* _Ryan Propper_, Jul 24 2005 *)
%Y Cf. A089328.
%K base,nonn
%O 1,2
%A _Amarnath Murthy_, Nov 04 2003
%E Corrected and extended by _Ryan Propper_, Jul 24 2005
%E More terms from _David Wasserman_, Sep 13 2005
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