Fibonacci number
![A tiling with squares whose side lengths are successive Fibonacci numbers](/Images/godic/202501/13/3421-FibonacciBlocks3455.png")
![The Fibonacci spiral: an approximation of the golden spiral created by drawing circular arcs connecting the opposite corners of squares in the Fibonacci tiling;[4] this one uses squares of sizes 1, 1, 2, 3, 5, 8, 13, 21, and 34.](/Images/godic/202501/13/Fibonacci_spiral_34.svg3455.png")
![A page of Fibonacci's Liber Abaci from the Biblioteca Nazionale di Firenze showing (in box on right) the Fibonacci sequence with the position in the sequence labeled in Latin and Roman numerals and the value in Hindu-Arabic numerals.](/Images/godic/202501/13/Liber_abbaci_magliab_f124r3455.jpg")
![The number of rabbits form the Fibonacci sequence](/Images/godic/202501/13/FibonacciRabbit.svg3455.png")
In mathematics, the Fibonacci numbers or Fibonacci sequence are the numbers in the following integer sequence:
or (often, in modern usage):
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.