Perfect Numbers

6 splits into 1, 2, and 3 — and 1 + 2 + 3 = 6. Its proper parts add back to exactly itself. The Pythagoreans called such numbers 'perfect' and revered 6 and 28. 2000 years later we've found only 52 of them, the largest millions of digits long — and we still don't know if a single odd perfect number exists. A simple definition, an open frontier.