Leonard of Pisa or Fibonacci played an important role in reviving ancient mathematics and made significant contributions of his own. Liber abaci introduced the Hindu-Arabic place-valued decimal system and the use of Arabic numerals into Europe.

The fibonacci sequence is easy to see that 1 pair will be produced the first month, and 1 pair also in the second month (since the new pair produced in the first month is not yet mature), and in the third month 2 pairs will be produced, one by the original pair and one by the pair which was produced in the first month. In the fourth month 3 pairs will be produced, and in the fifth month 5 pairs. After this things expand rapidly, and we get the following sequence of numbers:
1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, ...

FIbonacci sequence is explain as follow.........

1 Pair : we start with 1 pair of newly born rabbits

1 Pair : our rabbits take 1 month to mature

2 Pair : At the end of 2nd month, our rabbits produce 1 newly born pair, so that now we have 2 pairs of rabbits.

3 Pair : At the end of 3rd month, we have 3 pairs of rabbits (our original pair + 2 pairs of babies)

5 Pair : At the end of 4th month, 1 pair of babies of the original rabbits produce a newly born pair, while the other pair of babies mature, and our original rabbits produce another new pair. This gives us 5 pairs of rabbits.