Fibonacci number generator
The Fibonacci sequence from F0 = 0, each term the sum of the two before it. Up to 100 terms, every digit exact.
Output · 15 terms
ReadyEach Fibonacci number is the sum of the two before it. The ratio between consecutive terms approaches the golden ratio φ ≈ 1.618. Terms grow fast, so larger indices become very long integers.
- Terms
- Up to 100
- Precision
- Exact
Related tools
Guides
This Fibonacci number generator lists the sequence from F0 = 0 and F1 = 1, up to 100 terms. The last one it can show, F99, is 218,922,995,834,555,169,026, a 21-digit number. Ordinary JavaScript numbers can't hold values that big exactly (the first one they get wrong is F79), so the tool adds with BigInt and every digit you see is correct.
How to generate Fibonacci numbers
- Drag the How many terms slider anywhere from 1 to 100.
- The grid updates as you drag, starting at F0.
- Click any cell to copy that one number.
- Copy CSV gives index,value rows. Copy as list gives the numbers separated by commas.
How the Fibonacci sequence is defined
Start with F0 = 0 and F1 = 1. After that, F(n) = F(n-1) + F(n-2), so the sequence runs 0, 1, 1, 2, 3, 5, 8, 13, 21, 34. Each term is roughly 1.618 times the one before, which adds up fast. F78 = 8,944,394,323,791,464 still fits in a standard double. F79 = 14,472,334,024,676,221 is past 2^53, the point where doubles can no longer store every whole number, so a plain JavaScript loop starts printing wrong digits there.
Frequently asked questions
What is the Fibonacci sequence?
A list of numbers where each one is the sum of the two before it: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34 and on. Leonardo of Pisa, known as Fibonacci, used it in his 1202 book Liber Abaci in a puzzle about breeding rabbits.
Does the sequence start at 0 or 1?
This tool starts at F0 = 0, the usual convention today. Some textbooks start at F1 = 1, F2 = 1 and leave out the zero. The indexes are the same; the list just begins one term later.
How many Fibonacci numbers can I generate?
Up to 100 terms, F0 through F99. F99 has 21 digits.
What is the golden ratio connection?
Divide a term by the one before it and the answer creeps toward the golden ratio, φ ≈ 1.6180339887. By F20 ÷ F19 = 6765 ÷ 4181 you already get 1.618034, which matches φ to six decimal places.
Built and maintained by Bipul Kumar. Found a wrong number or a broken result? Tell me and I'll fix it.