You’re being Fibonacci’d! From a single cell or seed to all of mankind and galaxies, Fibonacci numbers appear in micro and macro phenomena of Nature, and sequences of these numbers can be found in the growth of every living thing, a fundamental magical coordination system that Nature’s seemingly random complexities have in common.

It appears in the way in which leaves grow around the stem of plants and petals of a flower, in the rings of a palm tree trunk, in the uniform distribution of sunflower seeds in the seed head, in the shape of hurricanes like Irene and spiral galaxies like Messier 74. Fibonacci numbers define the basis of our very existence as Nature’s own numbering system.

Though the so-called Fibonacci numbers have thus most probably existed since the very beginning of time, they came to widespread recognition thanks to an Italian man called Leonardo Pisano aka Leonardo of Pisa, his passion for maths and his humble desire to estimate how fast rabbits could breed in ideal circumstances.

In other words, the problem he was working on when he stumbled upon the sequence we know as Fibonacci was:

A certain man put a pair of rabbits in a place surrounded by a wall. How many pairs of rabbits can be produced from that pair in a year if it is supposed that every month each pair begets a new pair from which the second month on becomes productive?

(Liber Abaci)

As the son of a merchant, Guglielmo Bonaccio, Leonardo traveled widely in his youth and based on the knowledge he gained during his travels in Africa and the Near East, he wrote the Book of Calculation, the Liber Abaci in 1202, with the primary intention of introducing the decimal number system to the Latin-speaking world and through commercial and mathematical calculations providing practical solutions for Italian merchants and foreign traders dealing with different kinds of weights and money systems, making conversions less of a headache. Through his mathematical investigations, he arrived at an expression exemplified in his book as the rule of xn = xn-1 + xn-2 governing the sequence of 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, and so on, where the next number is found by adding up the two numbers before it, namely, the Fibonacci numbers. However, these numbers are said to have appeared much earlier, in the Hindu-Arabic arithmetic system, called the Virahanka numbers in Indian Mathematics. So, albeit Leonardo Pisano was not first to actually discover the Fibonacci numbers he is most well-known for, his Liber Abaci is definitely one of the first Western books to describe the eventual replacement of the Roman numerals, which happened later in the mid 13th century AD, and popularize the modern number system.

The first chapter of Part 1 begins:

These are the nine figures of the Indians: 9 8 7 6 5 4 3 2 1. With these nine figures, and with this sign 0 which in Arabic is called zephirum, any number can be written, as will be demonstrated.

And the rest is history, embedded in Golden Ratio, and the basis of having a day dedicated to all that’s Fibonacci.

But why in the world is it called Fibonacci? You remember Leonardo’s father was a Mr. Bonaccio? Well, the name Fibonacci was born out of a misinterpretation of part of the title of Leonardo’s Liber Abaci, which was hand-written since printing had not yet been invented back then yet, namely his surname of ‘filius Bonacci’ (‘son of Bonaccio’).

There’s a huge question left unanswered though. How to best celebrate Fibonacci Day? Go on a Fibonacci hunt, immerse yourself in the micro and macro cosmoses around you and discover the divine order all around. Are you spiraling yet?

Leonardo and the Liber Abaci

Leonardo Pisano, English Leonardo of Pisa, original name Leonardo Fibonacci (born c. 1170, Pisa?—died after 1240) medieval Italian mathematician who wrote Liber abaci (1202; “Book of the Abacus”), the first European work on Indian and Arabian mathematics.

Little is known about Leonardo’s life beyond the few facts given in his mathematical writings. During Leonardo’s boyhood his father, Guglielmo, a Pisan merchant, was appointed consul over the community of Pisan merchants in the North African port of Bugia (now Bejaïa, Alg.). Leonardo was sent to study calculation with an Arab master. He later went to Egypt, Syria, Greece, Sicily, and Provence, where he studied different numerical systems and methods of calculation.

When Leonardo’s Liber abaci first appeared, Hindu-Arabic numerals were known to only a few European intellectuals through translations of the writings of the 9th-century Arab mathematician al-Khwārizmī. The first seven chapters dealt with the notation, explaining the principle of place value, by which the position of a figure determines whether it is a unit, 10, 100, and so forth, and demonstrating the use of the numerals in arithmetical operations.

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