1
Input: 1 → [?] → 5, what is the rule? =
3
Input: 10 → [?] → 28, what is the rule? =
4
Input: 9 → [?] → 21, what is the rule? =
5
Input: 3 → [?] → 8, what is the rule? =
6
Input: 9 → [?] → 14, what is the rule? =
8
Input: 2 → [?] → 5, what is the rule? =