 Here, formula_74 is a suitably defined permutation and formula_75 refers to the path "P" with its coordinates permuted by formula_76.These paths give rise to two monotonic "n"-digit Gray codes formula_77 and formula_78 given by

The choice of formula_74 which ensures that these codes are indeed Gray codes turns out to be formula_81.The first few values of formula_66 are shown in the table below.