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A090147
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Primes of the form identical digits followed by a 7.
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1
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7, 17, 37, 47, 67, 97, 227, 337, 557, 887, 997, 1117, 4447, 5557, 8887, 11117, 333337, 555557, 666667, 888887, 11111117, 66666667, 222222227, 666666667, 888888887, 4444444447, 5555555557, 66666666667, 888888888887, 222222222222227
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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[ PadLeft[{7}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 18}], 1], PrimeQ[ # ] &]
Select[Union[Flatten[Table[FromDigits[PadLeft[{7}, n, d]], {n, 15}, {d, 9}]]], PrimeQ] (* Harvey P. Dale, Nov 15 2020 *)
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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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