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Search: id:A084366
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| A084366 |
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Numbers n such that the n-th prime number has an odd number of digits and becomes composite if the central digit is removed. |
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+0
1
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| 47, 49, 53, 54, 55, 58, 59, 60, 65, 70, 71, 72, 74, 75, 76, 77, 80, 81, 85, 87, 92, 95, 98, 100, 101, 102, 105, 106, 107, 112, 114, 117, 119, 120, 122, 124, 129, 134, 138, 139, 141, 142, 144, 148, 151, 152, 154, 156, 157, 158, 160, 162, 164, 166, 167
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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The 47th prime is 211, omitting the central digit yields 21, which is composite. The 59th prime is 277, omitting the central digit yields 27, which is composite.
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MATHEMATICA
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Select[Range[5, 1500], OddQ[Length[IntegerDigits[Prime[ # ]]]] && Not[PrimeQ[FromDigits[Drop[IntegerDigits[Prime[ # ]], {(Length[IntegerDigits[Prime[ # ]]] + 1)/2}]]]] &]
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CROSSREFS
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Adjacent sequences: A084363 A084364 A084365 this_sequence A084367 A084368 A084369
Sequence in context: A052352 A089553 A042103 this_sequence A128940 A141279 A106279
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KEYWORD
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base,nonn,less
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Jun 22 2003
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EXTENSIONS
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Edited by Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Sep 05 2007
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