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A127355
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Primes with prime digit counts. The digit count numerically summarizes the frequency of digits 0 through 9 in that order when they occur in a number.
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4
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3, 7, 17, 23, 71, 101, 103, 107, 109, 113, 127, 131, 137, 173, 199, 223, 233, 271, 311, 313, 317, 331, 359, 367, 409, 479, 499, 593, 673, 677, 701, 709, 773, 797, 907, 919, 929, 947, 953, 977, 991, 1009, 1123, 1129, 1193, 1213, 1217, 1223, 1231, 1277, 1291
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OFFSET
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1,1
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COMMENTS
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Compare with "Look And Say" version A056815.
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LINKS
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FORMULA
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EXAMPLE
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The primes 479,991,1747 respectively have digit counts 141719 (one 4,one 7,one 9), 1129 (one 1, two 9's), 111427 (one 1, one 4, two 7's) which are also prime; So they belong to the sequence.
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MATHEMATICA
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dc[n_] :=FromDigits@Flatten@Select[Table[{DigitCount[n, 10, k], k}, {k, 0, 9}], #[[1]] > 0 &]; Select[Prime@Range[210], PrimeQ[dc[ # ]] &] (* Ray Chandler, Jan 16 2007 *)
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PROG
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(Haskell)
a127355 n = a127355_list !! (n-1)
a127355_list = filter ((== 1) . a010051' . a047842) a000040_list
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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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EXTENSIONS
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STATUS
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approved
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