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 A120886 a(n) = number of k's with 1 <= k <= n where GCD(k,ceiling(n/k)) > 1. 2
 0, 0, 1, 1, 1, 1, 4, 4, 3, 2, 4, 4, 5, 5, 7, 8, 6, 6, 8, 8, 9, 9, 11, 11, 11, 10, 12, 10, 10, 10, 15, 15, 12, 13, 15, 15, 14, 14, 16, 16, 15, 15, 22, 22, 22, 22, 24, 24, 22, 21, 22, 23, 23, 23, 24, 24, 22, 22, 24, 24, 27, 27, 29, 27, 23, 23, 28, 28, 28, 29, 34, 34, 31, 31, 33, 32, 32 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,7 COMMENTS A120886(n) + A120887(n) = n. LINKS EXAMPLE a(7)=4 because for k=1,2,...,7 we have gcd(k,ceil(7/k))=1,2,3,2,1,2,1, respectively. MAPLE a:=proc(n) local ct, k: ct:=0: for k from 1 to n do if gcd(k, ceil(n/k))>1 then ct:=ct+1 else ct:=ct fi od: end: seq(a(n), n=1..87); # Emeric Deutsch, Jul 23 2006 MATHEMATICA Table[Length[Select[Table[GCD[k, Ceiling[n/k]], {k, 1, n}], # > 1 &]], {n, 1, 80}] (* Stefan Steinerberger, Jul 23 2006 *) CROSSREFS Cf. A120887. Sequence in context: A259259 A194668 A138160 * A228777 A023402 A073261 Adjacent sequences:  A120883 A120884 A120885 * A120887 A120888 A120889 KEYWORD nonn AUTHOR Leroy Quet, Jul 12 2006 EXTENSIONS More terms from Emeric Deutsch and Stefan Steinerberger Jul 23 2006 STATUS approved

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Last modified July 23 16:10 EDT 2019. Contains 325258 sequences. (Running on oeis4.)