The factors of 21 are 1, 3, 7, and 21 ... four factors.
The factors of 23 are 1 and 23 ... two factors.
The factors of 25 are 1, 5, and 25 ... three factors.
___________________________________
The factors of 12 are 1, 2, 3, 4, 6, and 12 ... six factors.
The factors of 18 are 1, 2, 3, 6, 9, and 18 ... six factors.