Can I make it so that an answer can only be used once?

Example:

Form user 1 enters "1452" as an answer and submits it

Form user 2 enters "785" as an answer and submits it

Form user 3 enters "1452" as an answer but is told that answer has already been used and cannot continue until another number has been chosen

Is that possible?

That's possible when you enable unique question to a field.

Here's a guide: http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question