# File lib/more/facets/math/factorial.rb, line 24
  def self.factorial(n)
    n = Integer(n)
    if n < 0
      nil
    elsif FACTORIALS.length > n
      FACTORIALS[n]
    else
      h = FACTORIALS.last
      (FACTORIALS.length .. n).each { |i| FACTORIALS.push h *= i }
      h
    end
  end