#### Nov 23

### Fibonacci Day

“A certain man had one pair of rabbits together in a certain enclosed place, and one wishes to know how many are created from the pair in one year when it is the nature of them in a single month to bear another pair."

~ Leonardo Bonacci (1175 – 1250)

The Italian Mathematician known as Fibonacci, is associated with the number series familiar to programming students everywhere. His interest in this number sequence (first described by Indian mathematicians in the 6th century) was based on his theoretical study of how fast rabbits could breed in ideal circumstances! Fibonacci Day is reckoned as November 23rd, from the digits "1, 1, 2, 3" , the first part of this recursive number sequence interpreted in a month/day format. Fibonacci numbers (in which subsequent numbers can be derived by adding the previous), are a natural sequencing which can be used to describe certain patterns in nature, often appearing in some leaf arrangement in plants, such as sunflowers and pinecone bracts. Though indeed favored by nature and with interesting mathematical properties, the Fibonacci sequence and its mathematical cousin (Phi, the "golden ratio") do not appear as widely as some have alleged, claiming their mysterious presence in art, architecture, human body proportions, etc ... . The purportedly ubiquitous nature of these "celebrity numbers" appears to be a bit of wishful "number gossip" generated by ardent, but not rigorously mathematical pattern seekers, and patiently debunked by mathematicians! Who knew? 1, 1, 2, 3, 5, 8, 13, 21, 34, ... 🐇 🐇 🐇 🐇 🐇

Fibonacci Day is celebrated November 23, using month-first notation 1-1-2-3, 11/23, based on the Fibonacci series begining 1, 1, 2, 3, 5, 8, ... a pattern of counting where each number is the sum of the previous two.

Fibonacci Day recognises the importance and value of Italian mathematician Leonardo Fibonacci’s contributions to mathematics and the prevalance of mathematics in the natural world.

The pattern and colour of stitches in the tartan are based on both the sequence and the colours of the Italian flag.

Leonardo of Pisa, sometimes known as Leonardo Fibonacci did not actually invent or discover the Fibonacci sequence (which first appears in Indian mathematics in connection with Sanskirt prosody), but he used it as an example in his book, Liber Abaci, when studying the idealized population growth of rabbits.

Fibonacci sequences appear in many biological settings - the branching in trees, the arrangement of leaves on a stem, the fruitlets of a pineapple, the flowering of artichoke, the uncurling of a fern, the arrangement of seeds in a pine cone, and much more.

For more on the Fibonacci sequence in nature, click the collage!