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Search: id:A120881
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| A120881 |
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a(n) = number of k's, for 1 <= k <= n, where GCD(k,floor(n/k)) > 1. |
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+0
2
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| 0, 0, 0, 1, 1, 0, 0, 2, 3, 2, 2, 2, 2, 1, 1, 4, 4, 4, 4, 5, 4, 3, 3, 5, 6, 5, 7, 8, 8, 3, 3, 7, 7, 6, 6, 8, 8, 7, 6, 9, 9, 6, 6, 7, 9, 8, 8, 11, 12, 12, 12, 13, 13, 14, 13, 15, 14, 13, 13, 11, 11, 10, 11, 16, 16, 12, 12, 13, 13, 10, 10, 15, 15, 14, 15, 16, 16, 13, 13, 17
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OFFSET
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1,8
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COMMENT
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A120881(n) + A120882(n) = n.
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EXAMPLE
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For n = 8, we have the pairs {k,floor(n/k)} of {1,8},{2,4},{3,2},{4,2},{5,1},{6,1},{7,1},{8,1}. From these pairs we get the GCD's of 1,2,1,2,1,1,1,1. 2 of these GCD's are > 1. So a(8)= 2.
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MATHEMATICA
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Table[Length[Select[Table[GCD[k, Floor[n/k]], {k, 1, n}], # > 1 &]], {n, 1, 80}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jul 23 2006
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CROSSREFS
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Cf. A120882.
Adjacent sequences: A120878 A120879 A120880 this_sequence A120882 A120883 A120884
Sequence in context: A128830 A090387 A030329 this_sequence A031217 A078545 A111497
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KEYWORD
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more,nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Jul 12 2006
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jul 23 2006
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