1: 3, 2
2:
3: 2
4: 2, 3
5: 3, 4
6: 8, 7
7: 9, 5
8: 12, 11, 10
9: 3, 4
10: 13, 4
11:
12: 9, 5
13: 2, 14
14: 2, 4
15: 6, 17, 16
16: 19, 18, 17
17: 9, 5, 11
18: 4, 3
19: 4, 3
20: 21, 15
21: 8, 7
22: 3
23: 8, 2, 24
24: 7, 25
25: 9, 5
26: 8
27: 13, 4