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Search: id:A039787
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| A039787 |
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Primes p such that p-1 is square-free. |
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14
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| 2, 3, 7, 11, 23, 31, 43, 47, 59, 67, 71, 79, 83, 103, 107, 131, 139, 167, 179, 191, 211, 223, 227, 239, 263, 283, 311, 331, 347, 359, 367, 383, 419, 431, 439, 443, 463, 467, 479, 499, 503, 547, 563, 571, 587, 599, 607, 619, 643, 647, 659, 683, 691, 719, 743
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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An equivalent definition: numbers n such that phi(n) is equal to the square-free kernel of n-1.
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EXAMPLE
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phi(43)=42, 42=2^1*3^1*7^1, 2*3*7=42.
p=223 is here because p-1=222=2*3*37
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MATHEMATICA
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lst={}; Do[p=Prime[n]; If[SquareFreeQ[Floor[p-1]]&&!SquareFreeQ[Floor[p+1]], AppendTo[lst, p]], {n, 6!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Dec 20 2008]
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CROSSREFS
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Cf. A000010, A007947.
Sequence in context: A165318 A108184 A049091 this_sequence A129940 A128631 A092217
Adjacent sequences: A039784 A039785 A039786 this_sequence A039788 A039789 A039790
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KEYWORD
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nonn
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AUTHOR
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Olivier Gerard (olivier.gerard(AT)gmail.com)
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EXTENSIONS
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More terms from Labos E. (labos(AT)ana.sote.hu)
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