Odd perfect numbers
Conjecture There is no odd perfect number.
There is substantial literature on the problem. Most proceeds from a study of the multiplicative function where the conjecture can be stated: implies that is even.
Bibliography
* indicates original appearance(s) of problem.
limiting divisors
My idea is to assume that the OPN is divisible by a prime number (e.x. 3) then use the properties of perfect numbers to figure out other numbers the OPN is divisible by.