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Search: id:A123565
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| A123565 |
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a(n) = number of positive integers k which are <= n and where k, k-1 and k+1 are each coprime to n. |
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1
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| 1, 0, 0, 0, 2, 0, 4, 0, 0, 0, 8, 0, 10, 0, 0, 0, 14, 0, 16, 0, 0, 0, 20, 0, 10, 0, 0, 0, 26, 0, 28, 0, 0, 0, 8, 0, 34, 0, 0, 0, 38, 0, 40, 0, 0, 0, 44, 0, 28, 0, 0, 0, 50, 0, 16, 0, 0, 0, 56, 0, 58, 0, 0, 0, 20, 0, 64, 0, 0, 0, 68, 0, 70, 0, 0, 0, 32, 0, 76, 0, 0, 0, 80, 0, 28, 0, 0, 0, 86, 0, 40, 0, 0
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OFFSET
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1,5
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COMMENT
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a(p) = p-3, p = odd prime. a(2n) = 0. a(3n) = 0.
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EXAMPLE
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The positive integers which are both coprime to 25 and are <= 25 are 1,2,3,4,6,7,
8,9,11,12,13,14,16,17,18,19,21,22,23,24. Of these integers there
are 10 integers k where (k-1) and (k+1) are also coprime to 25. (These
integers k are 2,3,7,8,12,13,17,18,22,23.) So a(25) = 10.
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MATHEMATICA
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f[n_] := Length[Select[Range[n], GCD[ #, n] == 1 && GCD[ # - 1, n] == 1 && GCD[ # + 1, n] == 1 &]]; Table[f[n], {n, 100}] (*Chandler*)
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CROSSREFS
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Sequence in context: A087263 A099894 A048298 this_sequence A081120 A102392 A051517
Adjacent sequences: A123562 A123563 A123564 this_sequence A123566 A123567 A123568
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Nov 12 2006
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Nov 19 2006
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