“A certain man put a pair of rabbits in a place surrounded on all sides 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 which from the second month on becomes productive?”

– Fibonacci

Answer: The resulting sequence is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, …