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A071000 Numbers n such that the denominator of sum(k=1,n,1/GCD(n,k)) equals n. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Does lim n -> infinity a(n)/n = 3/2 ?

LINKS

Table of n, a(n) for n=1..72.

EXAMPLE

sum(k=1,12,1/GCD(12,k))=77/12 hence 12 is in the sequence.

MATHEMATICA

Select[Range[100], Denominator[Sum[1/GCD[#, k], {k, #}]]==#&] (* Harvey P. Dale, Dec 13 2011 *)

PROG

(PARI) for(n=1, 300, if(denominator(sum(i=1, n, 1/gcd(n, i))) == n, print1(n, ", ")))

CROSSREFS

Sequence in context: A095410 A022293 A183218 * A088451 A047595 A079298

Adjacent sequences:  A070997 A070998 A070999 * A071001 A071002 A071003

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, May 18 2002

STATUS

approved

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Last modified November 21 14:12 EST 2014. Contains 249779 sequences.