All you have to do is multiply each term by 2:
1 = 3
2 = 6
3 = 12
4 = 24
5 = 48
6 = 96
7 = 192
8 = 384
9 = 768
10 = 1,536
11 = 3,072
12 = 6,144
13 = 12,288
14 = 24,576
15 = 49,152
16 = 98,304
17 = 196,608
18 = 393,216
19 = 786,432
20 = 1,572,864
The 20th term is 1,572,864.
Hope this helped☺☺