1
Input: 2 → [?] → 4, what is the rule? =
2
Input: 3 → [?] → 9, what is the rule? =
4
Input: 3 → [?] → 15, what is the rule? =
6
Input: 3 → [?] → 0, what is the rule? =
7
Input: 10 → [?] → 9, what is the rule? =
8
Input: 10 → [?] → 20, what is the rule? =