A prime number can be divided only by itself and one, so it is read as independence and integrity. In a dream it suggests a part of you that refuses to be broken down or shared out.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.