If a circle is centered on the origin and has radius r, it may pass through some points with integer coordinates. In fact, by symmetry, this will be a multiple of 4.

Find the smallest radius that will pass through 4n integer points where n=1,2,3,4,5.

Feel free to go further.

radius sqrt(5) is minimal.  It passes through (2,1) and (1,2)

Posted by Steve Herman on 2011-02-28 17:50:01