They are 1, 3, 9, 27.
8 of them.
The sum of the positive odd factors of 36 is 13 (1 + 3 + 9 = 13).
1, 3, 9, 27, 81.
The positive integer factors of 1017 are: 1, 3, 9, 113, 339, 1017
The positive integer factors of 261 are: 1, 3, 9, 29, 87, 261
The positive integer factors of 531 are: 1, 3, 9, 59, 177, 531
The positive integer factors of 1251 are: 1, 3, 9, 139, 417, 1251
The positive integer factors of 387 are: 1, 3, 9, 43, 129, 387
The positive integer factors of 3771 are: 1, 3, 9, 419, 1257, 3771
The positive integer factors of 81 are:1, 3, 9, 27, 81
The positive integer factors of 981 are: 1, 3, 9, 109, 327, 981