Number
Numbers, especially lower ones, have a "mythological" significance, such as three, four, and seven. Numbers have more of a qualitative meaning for the unconscious than a quantitative one. (See each respective number.)
Everyday Numbers
Numbers in dreams may refer to things we recognize from our daily life, such as phone numbers, street addresses, and so on. The dreamer's associations will certainly reveal this.
Time Period and Age
Numbers in dreams sometimes represent time periods. For example, if a dream includes the number 11, it may refer to something that happened eleven years ago; or the number 17 may symbolize something that happened or was relevant during the age of seventeen. (See also Time point.)
Masculine and Feminine Numbers
Even numbers have traditionally been viewed as feminine, passive, earthly, etc., while odd numbers have been considered masculine, dynamic, and so on, both in the East and the West. (Cf. Three and Four.)
Numbers as Symbols
It can be helpful to pay attention to numbers in dreams. For example, if you are riding a motorcycle with three wheels, going to a party on the second floor, or ending up in fourth place in a queue, this has a symbolic, meaningful quality (especially if the number is unexpected or particularly emphasized in the dream).