784 Reciprocal Pairs.sf

#!/usr/bin/ruby

# Reciprocal Pairs
# https://projecteuler.net/problem=784

func F(n) {

    var total = 0

    for a in (2 .. n) {
        var v = (a*a - 1)

        v.divisors.each {|d|
            d <= a || break

            var p = (a + d)
            var q = (a + v/d)

            if (p <= n) {
                total += p+q
            }
            else {
                break
            }
        }
    }

    return total
}

say F(5)
say F(10**2)
say F(2 * 1e6)