Calculate the nth Fibonacci number, with F₁ = 1 and F₂ = 1.
| Fₙ | – |
Use this calculator for the sequence 1, 1, 2, 3, 5, 8, … where each term is the sum of the two before it. Indexing starts at 1: F₁ = 1, F₂ = 1, F₁₀ = 55. Some texts set F₀ = 0 and F₁ = 1; this page does not return F₀.
n must be an integer from 1 to 78 so the result stays an exact IEEE integer. Larger n is refused. Binet’s formula is not used, so there is no rounding-to-nearest-integer step.
n: The 1-based index (1, 2, 3, …).
Fₙ: The nth Fibonacci number.
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