Happy Fibonacci Day - November 23 ... 11/23

November 23, 2017 is more than just Thanksgiving this year.  November 23 … or 11/23 … is a Math holiday.  It’s Fibonacci Day.  Allow us to explain…

A number sequence is an ordered list of numbers defined by a rule or function—the numbers in the list follow some sort of pattern. Each number in a sequence is called a term. The Fibonacci sequence is as follows: 0, 1, 1, 2, 3, 5, 8, 13…

Looking at the terms in the sequence above, can you guess why we celebrate Fibonacci Day on November 23?

Some fun facts about the Fibonacci sequence:

• The Fibonacci sequence is an infinite sequence—it has an unlimited number of terms and goes on indefinitely!
• In addition, it is a recursive sequence—it is defined by a list of a few terms and a rule or function for computing the rest of the sequence. The rule/formula goes as follows:

F0 = 0

F1 = 1

Fn = Fn-1 + Fn-2 for n > 1

… which means that after the first two terms, each term in the Fibonacci sequence is found by adding the two previous terms together. Can you figure out the next four terms in the Fibonacci sequence after 13?

The Fibonacci numbers are often seen in nature – from animals to plants -- the number of petals on a flower, the skin of a pineapple, and even the number of spirals in which sunflower seeds grow.

As an example, the innermost layer of an artichoke has one bract (a specialized leaf—the part of the artichoke you eat). The next layer has one, then the next has two, then three, then five, then eight, then 13, and so on! 

In addition, a way of representing the sequence underpins a spiral shape which is known as The Golden Ratio.

The Fibonacci spiral kind of looks like a seashell.

And when you draw the number out on paper using larger and larger squares to show each number, they create a spiral, like the kind you’d see in a sea shell or the center of a flower.

Mathematicians’ fascination with the Fibonacci sequence goes way back. Introduced to the Western world by a medieval Italian mathematician named (you guessed it) Fibonacci in 1202, the number sequence appeared in Indian mathematics as early as 200 BC.