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A231605
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The least number k such that the decimal number formed from 1 followed by n copies of k is prime.
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2
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1, 9, 7, 37, 9, 13, 9, 47, 7, 13, 11, 17, 7, 87, 3, 63, 147, 1, 67, 137, 21, 1, 23, 19, 163, 9, 9, 57, 371, 63, 51, 351, 17, 471, 89, 257, 39, 81, 109, 63, 3, 7, 973, 47, 39, 109, 737, 201, 429, 143, 7, 261, 9, 7, 129, 221, 69, 63, 167, 77, 493, 459, 587, 183, 129
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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For n = 2, the numbers to consider are 111, 122, 133, 144, 155, 166, 177, 188, 199,.... The first prime is 199.
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MATHEMATICA
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Table[k = 1; While[p = FromDigits[Join[{1}, Flatten[Table[IntegerDigits[k], {n}]]]]; ! PrimeQ[p], k = k + 2]; k, {n, 65}]
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CROSSREFS
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Cf. A112733 (smallest prime of the form 1 followed by n copies of k).
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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