16 has three factor pairs: (16,1)(8,2)(4,4)
One to one.
One doesn't have a factor pair.
Factor pairs are two numbers multiplied together to get one number. Examples: One factor pair of 24 is 4, 6. One factor pair of 70 is 5, 14. One factor pair of 144 is 12, 12.
The factor pairs of 29 are 1 and 29. 29 is prime so it has only one factor pair.
The factor pairs of 293 are 293 and 1. 293 is prime, so it has only one factor pair.
The difference is between factor pairs and distinct factors. With square numbers, one of the factor pairs will be the same number twice. When listing the distinct factors, that number is only listed once.
36, for one.