FibonacciCalc: Sequence Tool

FibonacciCalc works out Fibonacci numbers exactly, for students, teachers and anyone curious about the sequence and the golden ratio. Five tools on one screen:

• Terms: enter n from 0 to 500 and get the exact F(n), every digit included, with a preview of the sequence, the running sum and Fₙ / Fₙ₋₁ against φ
• Lookup: paste a number of up to 1,000 digits to see whether it is a Fibonacci number, its position, the Fibonacci numbers just below and above it, and its Zeckendorf decomposition
• Lucas & Custom: Lucas numbers or your own two starting values, any term from 0 to 10,000, with its digit count and the sum of the first n + 1 terms
• Convergence: watch Fₙ / Fₙ₋₁ close in on φ for up to 500 terms, in a table and in a line chart of the ratio or of the error
• Pisano: the period of the Fibonacci numbers modulo any m up to 1,000,000, with the first residues of the cycle
• Copy or share any result in full, every digit included
• Save named calculations with notes to reopen later