Generate Negafibonacci Numbers

Need a sequence that goes below zero? The Generate Negafibonacci Numbers tool creates symmetrical Fibonacci sequences that include negative indices. Unlike the regular Fibonacci series, the Negafibonacci version mirrors backward and flips signs as it extends. This is perfect when you’re exploring mathematical patterns, building recursive algorithms, or just want a clean left-right progression around zero.

You can generate any number of terms, add positive Fibonacci values if needed, and choose between list or comma-separated output all in one click.

Paste your input above or import a file below.
No file chosen
Supported file types: .txt, .csv, .tsv, .log, .json, .xml, .md, .ini, .yaml, .yml, .html, .htm, .css
Total items: 0
Options
Include positive Fibonacci
Reverse order
Comma-separated output

How to Use:

Enter how many terms you want in the input box. For example, typing 8 gives you the first 8 negative-index Fibonacci numbers, starting from -8 to -1. The result always includes zero in the center, since it acts as the symmetry point of the sequence.

Want to import a file instead? Click “Choose File” to upload a .txt, .csv, or other supported type. The accepted formats are listed just under the file input. Once your input is ready, the output updates live on the right.

Use the toggles in the Options box to control your sequence. You can:

  • Include the regular (positive) Fibonacci terms
  • Reverse the order of output
  • Show results as comma-separated values instead of one-per-line

As you adjust the settings, the result updates in real time. You’ll see a live item count below the output box. When you’re done, hit “Copy Output” or “Export to File” to save your sequence. Click “Clear All” to reset everything, including inputs and settings.

What Generate Negafibonacci Numbers can do:

This tool produces both negative and positive Fibonacci values around zero, known as a Negafibonacci sequence. The negative side uses the formula F(-n) = (–1)ⁿ⁺¹ × F(n), which flips the signs to maintain recursive symmetry. You get control over the direction and formatting, and everything updates instantly in the browser. No reloads, no waiting, no server calls.

Example:

Input:

8

Output (with all toggles ON):

21  
-13  
8  
-5  
3  
-2  
1  
0  
1  
1  
2  
3  
5  
8  
13  
21

Common Use Cases:

The Generate Negafibonacci Numbers tool is great for students, educators, or developers needing a mathematically balanced Fibonacci sequence. Whether you’re visualizing symmetry, prepping data for recursive functions, or experimenting with algorithms, this gives you exactly the format and flow you need. It’s fast, flexible, and works entirely offline.

Useful Tools & Suggestions:

Check out Generate Fibonacci Numbers to compare how flipping the index direction changes the sequence. And if you’re layering multiple results, Normalize Line Breaks in Text can make everything easier to read and line up.

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