Create a function that takes a number maxDen and returns the total number of fully simplified proper fractions that exist with denominator less than or equal to maxDen.
You only need to return the number of fractions; NOT the fractions themselves. In the examples below, I list the fractions simply for your reference.
simPropFrac(10) ➞ 31
// 1/2, 1/3, 2/3, 1/4, 3/4, 1/5, 2/5, 3/5, 4/5, 1/6, 5/6, 1/7, 2/7, 3/7, 4/7, 5/7, 6/7, 1/8, 3/8, 5/8, 7/8, 1/9, 2/9, 4/9, 5/9, 7/9, 8/9, 1/10, 3/10, 7/10, 9/10
simPropFrac(7) ➞ 17
// 1/2, 1/3, 2/3, 1/4, 3/4, 1/5, 2/5, 3/5, 4/5, 1/6, 5/6, 1/7, 2/7, 3/7, 4/7, 5/7, 6/7
A fully simplified proper fraction is a fraction where both the numerator and denominator share no common factors besides 1 and the fraction is less than 1.