The Fibonacci series is the required answer.
In mathematics, the Fibonacci numbers form a sequence defined by the following recurrence relation:
The nth number Fib(n) in the Fibonacci series, where ( n > = 1 ), is given by the following formula:
Fib(n) = 1 /

5 x [ { (1+

5)/2 }
n - { (1-

5)/2 }
n ]
If you prefer values in your formulae, then here is another form:-
| Fib(n) = | 1.6180339..n ? (?0.6180339..)n | |
 |
 2.236067977.. |
Well the Fibonacci series is the following:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987
i.e any number is the sum of the preceeding two numbers.
Cheers !!!