1, 2, 4, 8, 16.
they are 1,19
1 and 20, 2 and 10, 4 and 5
1,2,3,4,6,8,12,24
28,1,14,2,7,4
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
Composite
Its factors are: 1, 11, 101 and 1111
1, 3, 9, 27, 81