Leetcode 2992. Number of Self-Divisible Permutations

Count how many permutations of 1..n satisfy that for every position i the placed value and i are "self-divisible" (e.g., the value divides i or i divides the value). This requires exploring combinatorial assignments efficiently—typically via backtracking with pruning or bitmask DP—because n is small but the search space is factorial.