The Fibonacci Numbers
One special recursively defined function, which has no simple explicit
definition, yields the Fibonacci numbers:

The values of this function are:
| f (1) | = | 1 |
|
| f (2) | = | 1 |
|
| f (3) | = | 1 + 1 = 2 |
|
| f (4) | = | 1 + 2 = 3 |
|
| f (5) | = | 2 + 3 = 5 |
|
| f (6) | = | 3 + 5 = 8 |
|
| f (7) | = | 5 + 8 = 13 |
|
| f (8) | = | 8 + 13 = 21 |
|
| f (9) | = | 13 + 21 = 34 |
|
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Thus, the sequence of Fibonacci numbers is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55,
. These numbers have many interesting properties that will be studied in
higher math. They recur often in mathematics and even in nature.