Fibonacci number

fibonacci-number · version 1.0.0 · Numbers & math · free, no key needed

Compute the Fibonacci number at a zero-based index and return its exact decimal string.

Use when you need to: fibonacci number 90 · compute nth fibonacci number · exact fibonacci value.

Decide before calling

Read the versioned contract and the supported scope below. Reuse fibonacci-number@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use fibonacci-number@1.0.0 for fibonacci number 90. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

• fibonacci number 90
• compute nth fibonacci number
• exact fibonacci value
• fib number at index
• calculate fibonacci without rounding
• what is the 100th fibonacci number
• zero based fibonacci lookup

Not supported

• negative-index sequence extensions
• floating-point approximations
• unbounded sequence generation

Behavior

• F(0)=0, F(1)=1, and F(n)=F(n-1)+F(n-2).
• The index is zero-based and the result is an unsigned base-10 string.
• Standard version: OEIS A000045 (live entry retrieved 2026-11-05; NAME, initial terms, OFFSET 0,4); stable source URL: https://oeis.org/A000045.

Input

• index (integer, required): min 0; max 10000

Output

• index (integer, required): min 0; max 10000
• value (string, required): min length 1; max length 2091; pattern ^[0-9]+$
• standard_version (string, required): min length 1; max length 120

Limits

• max input bytes: 64
• max index: 10000
• max digits: 2090
• max iterations: 14
• max output bytes: 2300

Example

Request input:

{
  "index": 10
}

Response:

{
  "result": {
    "index": 10,
    "value": "55",
    "standard_version": "OEIS A000045 (live entry retrieved 2026-11-05; NAME, initial terms, OFFSET 0,4)"
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "fibonacci-number",
  "version": "1.0.0",
  "input": {
    "index": 10
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/fibonacci-number/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"index":10}'

The machine-readable contract is at /v1/tools/fibonacci-number/versions/1.0.0.

CLI

node cli.mjs run fibonacci-number 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

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