Writing the expansion in this non-linear way shows the expansion in a more understandable way. It also makes the connection with the tetrahedron obvious−the coefficients here match those of layer 4. All the implicit coefficients, variables, and exponents, which are normally not written, are also shown to illustrate another relationship with the tetrahedron. (Usually, "1"A"" is ""A""; ""B"1" is ""B""; and ""C"0" is "1"; etc.) The exponents of each term sum to the layer number ("n"), or 4, in this case. More significantly, the value of the coefficients of each term can be computed directly from the exponents. The formula is: , where "x, y, z" are the exponents of "A, B, C," respectively, and "!" means factorial (e.g.: ). The exponent formulas for the 4th layer are: