The cornerstone of modern math wouldn't be possible without the Hindu-Arabic numerical system. Breakthroughs, discoveries, and DIY tips sent every weekday. Most people know about Pi Day (3/14), but there are even rarer days on the calendar like Pythagorean Triple Square Day (9/16/25). The poetry of mathematics manifests everywhere in nature, but few numerical patterns are more common than the Fibonacci Sequence . First described in 1202 by mathematician Italian Leonardo Bonacci (Fibonacci is a shortening of or "son of Bonacci"), the concept involves adding 1 and 1 together, then doing the same for every successive pair of numbers.