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A120882
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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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3
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1, 2, 3, 3, 4, 6, 7, 6, 6, 8, 9, 10, 11, 13, 14, 12, 13, 14, 15, 15, 17, 19, 20, 19, 19, 21, 20, 20, 21, 27, 28, 25, 26, 28, 29, 28, 29, 31, 33, 31, 32, 36, 37, 37, 36, 38, 39, 37, 37, 38, 39, 39, 40, 40, 42, 41, 43, 45, 46, 49, 50, 52, 52, 48, 49, 54, 55, 55, 56, 60, 61, 57, 58
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A120881(n) + A120882(n) = n.
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EXAMPLE
| 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. 6 of these GCD's are = 1. So a(8) = 6.
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MAPLE
| a:=proc(n) local ct, k: ct:=0: for k from 1 to n do if gcd(k, floor(n/k))=1 then ct:=ct+1 else ct:=ct: fi: od: ct; end: seq(a(n), n=1..85); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Jul 24 2006
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MATHEMATICA
| 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
| Cf. A120881.
Sequence in context: A162627 A188215 A023158 * A102187 A133610 A029033
Adjacent sequences: A120879 A120880 A120881 * A120883 A120884 A120885
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Jul 12 2006
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) and Ryan Propper (rpropper(AT)stanford.edu), Jul 23 2006
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