What are its aliquot parts?
We have 1, 2, 4, 71, and 142. When you add these five together, you get 220. Bingo. Thus 220 and 284 are said to be amicable or “friendly” numbers. These are really rare, and Pythagoras probably thought he had discovered the only such pair. Oh, by the way, just to show you how jealous amiable was, sometime in the 18th or 19th century amiable tried to hijack the concept from amicable, so that there are attestations of amiable numbers in English, but amicable quickly beat off the challenge. Thus, to this day, you will find about 10X as many Internet entries for amicable numbers as you will of amiable numbers. The rebellion obviously was put down, but not without bloodshed. Other Amicable Numbers Even though Pythagoras discovered these amicable numbers long ago, mathematicians have not given the concept a rest. Driven by no financial considerations or interests in utility at all, modern mathematicians have discovered other amicable numbers. As one Internet source says: “It was not until 1
