For general information about multiperfect numbers (MPFNs), please see my main MPFN page. For a formal definition, see the glossary.
For some of the history and theory of perfect numbers and Mersenne primes, see Chris Caldwell's page on the subject.
For general knowledge about number theory, I highly recommend "An
Introduction to the Theory of Numbers", 5th ed., by G.H. Hardy and
E.M. Wright. Chapters 16 and 18 are particularly relevant to perfect
and multiperfect numbers. It's available in a comparatively
inexpensive paperback edition from Oxford University Press. You can
it online from Best
Book Buys, but you can probably get it quicker from your local university