What this calculator does
Fibonacci sequence works out the nth Fibonacci number, the sequence around it and the sum so far. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaF(0)=0, F(1)=1, F(n)=F(n−1)+F(n−2); sum of F(0)..F(n) = F(n+2) − 1
The inputs explained
| Field | What to enter |
|---|---|
| Term index n (F(0), F(1), …) | A number. Starts at 10. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with term index n (f(0), f(1), …)
Every other input is held at the calculator’s starting values while term index n (f(0), f(1), …) varies. Select any row to load that scenario into the calculator.
How the answer changes with term index n (f(0), f(1), …)