A_n^{\times}=A_{n-1}^=\cdot\frac 1 3\cdot\frac 2 4+A_{n-1}^{\bullet}\cdot\frac 1 3\cdot\frac 1 4=\frac 1 6A_{n-1}^=+\frac 1{12}A_{n-1}^{\bullet}