In one number, which is equal to the sum of all of its possible divisors (without herself) is, the Greeks sensed a secret. The first of these numbers is 6; 6 lets through 1, 2 and 3 share: 1 + 2 + 3 = 6. Such a number they called an ideal number.
The next ideal number is 28; 1 + 2 + 4 + 7 + 14 = 28. The Greeks discovered the first four ideal numbers: 6, 28, 496 and 8128. First 1500 Years later, the fifth ideal number was found. she is 33 550 336. The sixth ideal number is 8 589 869 056. To date, a total of 17 discovered ideal numbers. The last one is so long — she has 1373 digits —, that it would take up more than half a page.