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