Liber Abaci is a book that Leonardo Fibonacci wrote in 1202. In it Fibonacci introduces the so-called modus Indorum (method of the Indians), today known as the Arabic numerals. It shows the practical importance of the new numeral system, using lattice multiplication and Egyptian fractions, by applying it to commercial bookkeeping, conversion of weights and measures, the calculation of interest, money-changing, and other applications. Liber Abaci also posed, and solved, a problem involving the growth of a hypothetical population of rabbits based on idealized assumptions. The solution, generation by generation, was a sequence of numbers later known as the Fibonacci numbers. In the Fibonacci sequence of numbers, each number after the first two, is the sum of the previous two numbers. The sequence is 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, etc. The higher the sequence, the closer two consecutive numbers of the sequence divided by each other will approach the golden ratio ( approximately 1 : 1. 618 or 0.618 : 1).
Leonardo became a guest of the Emperor Frederick II, who enjoyed mathematicians and science. In 1240 the Republic of Pisa honored Leonardo by granting him a salary. In the 19th century, a