1, 1, 2, 3: It s Fibonacci Day! © Moab Republic/Shutterstock

Today"s date, November 23, can be represented as 11/23, or 1, 1, 2, 3—the beginning of the Fibonacci sequence of numbers. Likewise, as the leaves on the Queen Victoria agave in today"s image spiral out from the center, they also express the Fibonacci sequence. This unique sequence of numbers was introduced to Europe in 1202 by the Italian mathematician Leonardo of Pisa (posthumously named Fibonacci) in his revolutionary work, the "Liber Abaci." The book begins by describing the Hindu-Arabic numeral system or "Modus Indorum’—0 1 2 3 4 5 6 7 8 9—and shows how its application could simplify trade and make calculations faster and easier (most of Europe at this time used Roman numerals).