634 Numbers of the form a^2b^3.sf

#!/usr/bin/ruby

# Numbers of the form a^2 * b^3, where a,b > 1.
# https://projecteuler.net/problem=634

# Using the method posted by al13n.

# Runtime: 14.038s (previously 22 seconds).

func F(n) {
    var count = 0

    2..n.iroot(3) -> each_squarefree {|k|
        count += isqrt(idiv(n, k**3))-1
    }

    2..n.iroot(6) -> each {|k|
        count += 3.powerfree_count(isqrt(idiv(n, k**6)))
    }

    count -= prime_count(iroot(n, 6))
    count
}

F(2 * 1e4) == 130   || die "error"
F(3 * 1e6) == 2014  || die "error"
F(5 * 1e9) == 91255 || die "error"

say F(9 * 1e18)