These are the number of combinations which the CCubes algorithm (Dusa, 2018) checks
to determine the prime implicants from a minimization process.
In the bottom-up approach, CCubes first checks for single conditions (combinations of
both presence and absence, or more levels if multi-value), then all possible combinations
of levels for two conditions etc.
The precise equation that partitions the search space into complexity layers is:
$$
\sum_{c = 1}^{k} {k\choose c} \prod_{s = 1}^{c} l_s
$$
where \(l\) stands for the number of levels for each combination of \(c\)
conditions out of \(k\).