A000396 (OEIS entry for Perfect numbers)

A000396 refers to the sequence of perfect numbers, which are special whole numbers that equal the sum of their proper divisors (excluding themselves). The first few perfect numbers are 6, 28, and 496. For instance, the proper divisors of 28 are 1, 2, 4, 7, and 14, which sum to 28. Perfect numbers are rare and have interesting connections to prime numbers through a mathematical relationship established by Euclid. Their study provides insight into the nature of numbers and has fascinated mathematicians for centuries, often linking to concepts in number theory and abstract mathematics.