1, 2, 4, 8, 16.
they are 1,19
1 and 20, 2 and 10, 4 and 5
28,1,14,2,7,4
1,2,3,4,6,8,12,24
1 and 13 that's it
3 and 107
No.
1, 2, 4, 5, 8, 10, 16, 20, 25, 40, 50, 80, 100, 200, and 400
26, 1, 13, 2,6
1, 3, 9, 27, 81
Composite
Its factors are: 1, 11, 101 and 1111