Bill Bonacci represented the commercial interests of the merchants of Pisa in Bejaia, a Mediterranean port in northeastern Algeria. In that capacity he introduced his son Leonardo, while still a child, to principles of accounting with an eye to Leonardo’s future employment.

Leonardo was introduced to teachers of accounting and soon learned the practices of a wide variety of regions including Egypt, Syria, Greece, Sicily and Provence. He was especially attracted to the numerical notational systems of the Hindus and Arabs and in his early 30’s, when he had returned to Pisa, he wrote a book on the art of calculation.

This book “Liber Abaci” influenced the accounting practices of business in Italy and Europe in general and the numerical notation system Leonardo introduced gradually become the *de facto* standard for book keeping and accounting.

In his book there are many contrived scenarios whose function seems mainly to introduce a variety of numerical calculations so that readers could practice the novel numeration systems.

One problem in Leonardo’s book so intrigued people that it has become a favorite of almost all people who think even a little about mathematics.

Leonardo was enchanted by the fact that male drone bees are born from a queen bee’s unfertilized egg, so a male drone bee has no father. Female bees have both a mother and a father. So if one looks at the family tree of a male drone bee one sees something like this:

Parents | 1 |

Grandparents | 2 |

Great grandparents | 3 |

Great-great grandparents | 5 |

Great-great-great grandparents | 8 |

Leonardo said to himself: “Un giorno questi numeri sbloccheranno il segreto della natura e spiegheranno perché un drone non ha un padre”

(“Someday these numbers will unlock the secret of nature and will explain why a drone does not have a father”)

In his book he continued this backward calculation of the number of drone ancestors, but changed the setting of the problem. Maybe because it was getting difficult to name the ancestors beyond great-great-great-grandparents, or perhaps for some other reason, Leonardo changed this real scenario into an imaginary one of rabbits breeding, and counted the number of rabbits alive at discrete units of time, so inventing (but not for the first time in history) the famous Fi-bonacci sequence.