require "test/unit"

Z=->n{[*2..n].select{|r|(2...r).all?{|m|r%m>0}}.combination(2).count{|a,b|a*b<=n}}

class SquarefreeSemiPrimeCountTests < Test::Unit::TestCase
  def test_correct_count
	assert_equal 0, Z[1]
	assert_equal 18, Z[62]
	assert_equal 124, Z[420]
	assert_equal 2600, Z[10000]
  end
end