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API · /collatz-api

Collatz Sequence API

healthy 4,833 Subscribers

The Collatz conjecture (the "3n+1" or hailstone problem) as an API, computed locally and deterministically. Give it any positive integer and the sequence endpoint returns the full hailstone path — at each step an even number is halved and an odd number is tripled and incremented (3n+1) — together with the total stopping time (the number of steps to reach 1) and the peak value the sequence climbs to. Starting from 6 the path is 6, 3, 10, 5, 16, 8, 4, 2, 1 — eight steps, peaking at 16; the notoriously long start 27 takes 111 steps and soars to a peak of 9232 before collapsing. The steps endpoint returns just the stopping time and peak altitude without the whole path, for fast bulk scans of where the big climbs and long tails are. All arithmetic runs in arbitrary-precision integers so the peak stays exact even when a small starting number balloons into the millions, and a safety cap keeps every request bounded. Starting numbers up to one hundred trillion are accepted. Everything is computed locally and deterministically, so it is instant and private. Ideal for maths-education, number-theory, recreational-mathematics and puzzle app developers, sequence-and-hailstone visualisers, and teaching material on the most famous unsolved problem in arithmetic. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 2 compute endpoints. This is the Collatz/3n+1 sequence specifically; for prime factorisation or GCD use a number-theory API.

#collatz #3n-plus-1 #hailstone #number-theory #mathematics #developer-tools
api.oanor.com/collatz-api
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Machine-readable spec so AI agents can integrate this API.

/api/collatz-api/openapi.json
/api/collatz-api/llms.txt

Discovery: GET /api/index.json lists every API.

API health

healthy
Uptime
100.00%
Server probes · 24h
Avg latency
157 ms
Server probes · 24h
Subscribers
4,833
active
Total calls
57
last 7 days
status Full status page → · 9 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

Free

  • 4,350 calls / month
  • 2 requests / second
  • Hard cap (429 above quota, no overage)
  • 4,350 calls/month
  • 2 req/sec
  • Full sequence + stopping time + peak
  • No credit card
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Starter

€3.75 /month

  • 43,500 calls / month
  • 6 requests / second
  • Hard cap (429 above quota, no overage)
  • 43,500 calls/month
  • 6 req/sec
  • BigInt-exact peaks up to 1e14
  • Email support
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Pro

€10.80 /month

  • 224,000 calls / month
  • 15 requests / second
  • Hard cap (429 above quota, no overage)
  • 224,000 calls/month
  • 15 req/sec
  • Bulk hailstone scans
  • Priority support
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Mega

€35.50 /month

  • 1,240,000 calls / month
  • 40 requests / second
  • Hard cap (429 above quota, no overage)
  • 1,240,000 calls/month
  • 40 req/sec
  • Platform scale
  • Dedicated SLA
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An integer toolkit as an API. Factorize any number into its prime factors with exponents (and a readable 2^3 × 3^2 × 5 form), with the divisor count, the divisor sum, the full list of divisors and whether the number is perfect; find the greatest common divisor and least common multiple of two numbers (and whether they are coprime); and test primality, returning the next and previous prime. Handles numbers up to a trillion. Perfect for maths education and puzzles, cryptography demos, generating test data and any time you need the building blocks of a number. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 4 endpoints. A focused integer toolkit, distinct from a general math-expression engine.

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api.oanor.com/proglang-api

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The canonical MIME / media-type database (the jshttp mime-db used by Express and most of the Node ecosystem: IANA + Apache + nginx), served from memory — no key. Resolve a media type to its file extensions, charset and compressibility; reverse-lookup the media type(s) for a file extension (e.g. png → image/png); and search or list types by source. 2,600+ media types, 1,000+ with file extensions. Lean, predictable JSON. Ideal for upload validation, Content-Type resolution, file-type detection, download handlers and developer tooling.

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api.oanor.com/musicbrainz-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Collatz Sequence API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Collatz Sequence API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Collatz Sequence API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Collatz Sequence API cost?
Collatz Sequence API has a free tier with 100 calls / month. Paid plans start at €3.75 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Collatz Sequence API GDPR-compliant?
All requests to Collatz Sequence API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.

Pick an endpoint from the list on the left to see its details and try it.

Code snippets

Sign up to get an API key, then call any path under your slug.

curl https://api.oanor.com/collatz-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."
const res = await fetch("https://api.oanor.com/collatz-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();
$ch = curl_init("https://api.oanor.com/collatz-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);
import requests
r = requests.get(
    "https://api.oanor.com/collatz-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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