At the end after Nick explains to the woman, who would have been the last victim, their plan to catch the killer in her apartment, she faints. However, as she begins falling, her glasses start to fall off. She motions to keep them on her head.
When we first see the January victim enter her apartment, she is walking down a hallway with a bare floor. In the next scene where we see her, there is a rug on the hallway floor.
As a matter of definition, the integer 1 (one) is not a prime.
When Allison was strangled (and later died) in the beginning of the movie, there isn't a bruise marked on her neck from the ribbon that the strangler was using.