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A071000
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Numbers n such that the denominator of sum(k=1,n,1/GCD(n,k)) equals n.
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0
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1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 34, 36, 37, 38, 39, 40, 41, 43, 46, 47, 49, 50, 52, 53, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 67, 68, 71, 72, 73, 74, 75, 76, 77, 79, 80, 81, 82, 83, 85, 86, 88, 89, 91, 92, 93
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OFFSET
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1,2
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COMMENTS
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Does lim n -> infinity a(n)/n = 3/2 ?
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LINKS
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Table of n, a(n) for n=1..72.
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EXAMPLE
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sum(k=1,12,1/GCD(12,k))=77/12 hence 12 is in the sequence.
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MATHEMATICA
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Select[Range[100], Denominator[Sum[1/GCD[#, k], {k, #}]]==#&] (* From Harvey P. Dale, Dec 13 2011 *)
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PROG
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(PARI) for(n=1, 300, if(denominator(sum(i=1, n, 1/gcd(n, i))) == n, print1(n, ", ")))
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CROSSREFS
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Sequence in context: A095410 A022293 A183218 * A088451 A047595 A079298
Adjacent sequences: A070997 A070998 A070999 * A071001 A071002 A071003
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre, May 18 2002
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STATUS
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approved
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