Statistics by Wolfgang Creyaufmueller, including many tables and links to factoring sites and software.

Harry J. Smith's pages of the mathematics behind perfect numbers, aliquot sequences and Mersenne numbers. Includes program listings and e-mail archives.

Aliquot sequences arise in iterating the sum-of-divisors function s. Bosma has calculated tables up to start value 50,000 and 80 digits.

Status of various factorisations that would extend the known area of non-existence of odd perfect numbers, by Kevin Hare.

Definitions and references.

Sequences with initial term up to 10,000, by Christophe Clavier.

Data for various kinds up to 10^12, including unitary, infinitary, exponential, augmented and reduced varieties.

Up-to-date information on multiperfect numbers and searchable database maintained by Achim Flammenkamp.

Observations on amicable pairs and their distribution, including Harshad and Happy Amicable pairs.

J. L. Pe introduces perfect numbers relative to an arithmetical function f. Under this scheme, the usual perfect numbers are just one among many species of "f-perfect numbers". Several open problems and examples of perfect number sets are given, as well as a few f-amicable pairs.