Art of Problem Solving

1988 IMO Problems/Problem 3: Difference between revisions

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A function <math>f</math> is defined on the positive integers by
A function <math>f</math> is defined on the positive integers by
<math> f(1) = 1, f(3) = 3, f (2n) = f (n)</math> ,
<math> f(1) = 1, f(3) = 3, f (2n) = f (n)</math> ,
<math> f(4n+1) = 2f(2n+1)−f(n), f(4n+3) = 3f(2n+1)−2f(n)</math> ,
<math> f(4n+1) = 2f(2n+1)−f(n)</math>, <math>f(4n+3) = 3f(2n+1)−2f(n)</math> ,
for all positive integers <math> n</math> .
for all positive integers <math> n</math> .
Determine the number of positive integers <math> n</math> , less than or equal to <math> 1988</math> , for which <math> f(n) = n</math>  
Determine the number of positive integers <math> n</math> , less than or equal to <math> 1988</math> , for which <math> f(n) = n</math>  
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Revision as of 13:22, 7 June 2019

A function $f$ is defined on the positive integers by $f(1) = 1, f(3) = 3, f (2n) = f (n)$ , $f(4n+1) = 2f(2n+1)−f(n)$ (Error compiling LaTeX. Unknown error_msg), $f(4n+3) = 3f(2n+1)−2f(n)$ (Error compiling LaTeX. Unknown error_msg) , for all positive integers $n$ . Determine the number of positive integers $n$ , less than or equal to $1988$ , for which $f(n) = n$ .