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A127177
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Primes whose "Look And Say" descriptions from right to left (in the sense of method A, i.e., frequency followed by digit-indication) are also primes.
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2
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3, 7, 71, 103, 113, 163, 173, 311, 313, 331, 337, 349, 373, 757, 773, 797, 919, 953, 977, 991, 1109, 1123, 1151, 1171, 1181, 1213, 1237, 1277, 1279, 1297, 1327, 1423, 1447, 1543, 1553, 1567, 1621, 1663, 1669, 1747, 1811, 1873, 1877, 1889, 1993, 1999, 3049
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OFFSET
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1,1
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LINKS
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EXAMPLE
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71, 331 and 1277, for instance, belong to the sequence because their respective descriptions 1171 (one 1, one 7), 1123 (one 1, two 3's) and 271211 (two 7's, one 2, one 1) are primes.
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MATHEMATICA
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LookAndSayA[ n_] := FromDigits@Flatten@((Through[ {Length, First}[ # ] ] &) /@ Split@Reverse@IntegerDigits@n); Select[Prime@Range[450], PrimeQ@LookAndSayA@# &] (* Ray Chandler, Jan 16 2007 *)
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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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