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A090150
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Primes of the form a string of identical digits preceded by a 2.
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2
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2, 23, 29, 211, 233, 277, 2111, 2333, 2777, 2999, 23333, 2999999, 29999999, 2777777777, 23333333333, 2111111111111, 2777777777777777, 23333333333333333, 2111111111111111111, 2777777777777777777
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Select[ FromDigits /@ Flatten[ Table[ PadRight[{2}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 23}], 1], PrimeQ[ # ] &]
Select[Union[Flatten[Table[FromDigits[PadRight[{2}, n, d]], {n, 20}, {d, {1, 3, 7, 9}}]]], PrimeQ] (* Harvey P. Dale, Aug 25 2016 *)
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CROSSREFS
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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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