Consider the following situation. A problem, dating back to the early 13th century, posed by Leonardo Fibonacci asks how many rabbits you would have if you started with just two and let them reproduce. Assume that a pair of rabbits produces a pair of offspring each month and that each pair of rabbits produces their first offspring at the age of 2 months. Month by month the number of pairs of rabbits is given by the sum of the rabbits in the two proceeding months, except for the 0th and the Ist months.

After just 16 months, you have nearly 1600 pairs of rabbits !