Fuente TeX:

\sum_{k_1=0}^{c_A}\sum_{k_2=0}^{c_B}\sum_{k_3=0}^{c_C}\binom{n}{k_1}\binom{n-k_1}{k_2}\binom{n-k_1-k_2}{k_3}(\#\bar{A}\bar{B}\bar{C})^{n-k_1-k_2-k_3}