
Best Approximations
Problem 192
Published on Saturday, 3rd May 2008, 05:00 am; Solved by 825Let x be a real number.
A best approximation to x for the denominator bound d is a rational number r/s in reduced form, with s
d, such that any rational number which is closer to x than r/s has a denominator larger than d:
|p/q-x|
|r/s-x|
q
d
For example, the best approximation to
13 for the denominator bound 20 is 18/5 and the best approximation to
13 for the denominator bound 30 is 101/28.
Find the sum of all denominators of the best approximations to
n for the denominator bound 1012, where n is not a perfect square and 1
n
100000.