The Fibonacci Sequence is the series of numbers:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...
In this sequence, every number after the first two is the sum of the two preceding ones.
By definition, the first two numbers in the Fibonacci sequence are either 1 and 1, or 0 and 1, depending on the chosen starting point of the sequence, and each subsequent number is the sum of the previous two.
The sequence Fn of Fibonacci numbers is defined by the recurrence relation :
Fn = Fn-1 + Fn-2
with seed values :
F1 = 1 and F2 = 1
or
F0 = 0 and F1 = 1