In mathematics, the Fibonacci numbers are a sequence of numbers named after Leonardo of Pisa, known as Fibonacci. Fibonacci's 1202 book Liber Abaci introduced the sequence to Western European mathematics, although the sequence had been previously described in Indian mathematics.

The first number of the sequence is 0, the second number is 1, and each subsequent number is equal to the sum of the previous two numbers of the sequence itself. In mathematical terms, it is defined by the following recurrence relation:

That is, after two starting values, each number is the sum of the two preceding numbers. The first twenty Fibonacci numbers of the sequence are: 0,1,1,2,3,5,8,13,21,34,55,89, 144,233,377,610,987,1597,2584,4181,6765

 

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Fibonacci numbers
Leonardo of Pisa
Liber Abaci
Golden spiral