# File lib/facets/core/enumerable/permutation.rb, line 10
    def permutation(number)
        arr = to_a
        out = arr[0..0]
        nextfactor = factor = 1
        arr.each_with_index {|x,i|
            case i
            when 0: next
            else
                nextfactor = factor * (i+1)
                out.insert(number % nextfactor / factor, x)
                factor = nextfactor
            end
        }
        out
    end