Calculator that checks if a number is in the Fibonacci sequence

Use the calculator below to check if almost any number is a Fibonacci one.

What is a Fibonacci number?

A Fibonacci number should obey this sequence of numbers:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

The first Fibonacci number (F₀) is zero and, the second (F₁) and the third (F₁) are one.

To get the next Fibonacci number, we just need to add up the two numbers before it. For Example:

• The 4th (F₃) is found by adding the two numbers before it (1+1)
• The 5th (F₂) is also found by adding the two numbers before it (1+2);
• The 6th (F₄) is 2+3 = 5
• ...
• The 10th (F₉) is (13+21) = 34

and so on ...

You get the idea!

So, we can derive the following formula to calculate any Fibonacci number:

Fibonacci Chart

n	Fn
0	0
1	1
2	1
3	2
4	3
5	5
6	8
7	13
8	21
9	34
10	55
11	89
12	144
13	233
14	377
15	610

The fibonacii sequence grows very fast. For example:

F₀ = 0,
F₁₀ = 34,
F₂₀ = 4181,
F₃₀ = 514229,
F₄₀ = 63245986,
F₅₀ = 7778742049,
F₁₀₀ = 218922995834555169026,
F₂₀₀ = 173402521172797813159685037284371942044301,
F₅₀₀ = 86168291600238450732788312165664788095941068326060883324529903470149056115823592713458328176574447204501,
F₁₀₀₀ = 26863810024485359386146727202142923967616609318986952340123175997617981700247881689338369654483356564191827856161443356312976673642210350324634850410377680367334151172899169723197082763985615764450078474174626,
You get the idea!

That is why the best way to work with Fibonacci numbers is by using a calculator or a table.

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