The Fibonacci sequence starts 0, 1 and each next term is the sum of the two before it: 0, 1, 1, 2, 3, 5, 8, 13… It appears across nature, art and computer science.
Enter n to get the nth term, check whether any number belongs to the sequence, and see the first n terms at once. Large terms use exact big-integer arithmetic, so there is no rounding.
You can compute up to n = 1000 instantly, with exact integer results — no floating-point rounding.
As n grows, F(n)/F(n−1) approaches the golden ratio φ ≈ 1.618034.
Yes. Everything runs in your browser — nothing is uploaded.
Compute any Fibonacci term, check whether a number belongs to the sequence, and list the first N terms — with exact big-integer results. Runs entirely in your browser; nothing is uploaded.