What rule do the following three-numbered sequences follow? 2, 4, 8; 3,7,15; 5,20,380; 6,9,12?

1)
2, 4, 8 follows the rule: 2^k , k = 1, 2, 3. Successors are: 16, 32, 64 ...;k = 4, 5, 6
or
the other rule: successor := predecessor * 2
2)
3, 7, 15 follows the rule 2^k -1; for k = 2, 3, 4. Successors are: 31, 63, 127; k = 5, 6, 7
or
the other rule: successor := predecessor + (predecessor +1)
3)
5, 20, 380 follows the rule: successor := predecessor * (predecessor - 1)
e. g.: 20 = 5 * (5 - 1)