Open Problems

From the Wikipedia article at http://en.wikipedia.org/wiki/Open_problem

"An open problem is a problem that can be formally stated and for which a solution is known to exist but which has not yet been solved. It is common in graduate schools to point out open problems to students. These students as well as faculty members engage in research to solve such problems. Examples of problems that have been closed, or solved, by faculty members in the late twentieth century are Fermat's last theorem and the Four color theorem."

More Information

List of unsolved problems at http://en.wikipedia.org/wiki/List_of_unsolved_problems

Database of open problems at http://www.uia.org/encyclopedia/