Fibonacci's Problem:
"Start with a pair of rabbits, (one male and one female) born on January 1. Assume that all months are of equal length and that :
1. rabbits begin to produce young two months after their own birth;
2. after reaching the age of two months, each pair produces a mixed pair, (one male, one female), and then another mixed pair each month thereafter; and
3. no rabbit dies.
How many pairs of rabbits will there be after one year?"
