Number theory is a good source of unsolved problems that don’t require much background to understand. For example: http://en.wikipedia.org/wiki/List_of_unsolve

Number theory is a good source of unsolved problems that don’t require much background to understand. For example: http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_mathematics#Number_theory:_prime_numbers http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_ma...