Public JSON API

Numbers API

Everything you wanted to know about a number.

GET https://numbers.dk/api/42

{
    "number": 42,
    "formatted": "42",
    "previous": {
        "number": 41,
        "url": "https://numbers.dk/api/41"
    },
    "next": {
        "number": 43,
        "url": "https://numbers.dk/api/43"
    },
    "absolute": 42,
    "sign": 1,
    "even": true,
    "odd": false,
    "prime": false,
    "positive": true,
    "negative": false,
    "zero": false,
    "square": false,
    "cube": false,
    "fibonacci": false,
    "triangular": false,
    "palindrome": false,
    "digit_count": 2,
    "digit_sum": 6,
    "reversed": 24,
    "divisors": [
        1,
        2,
        3,
        6,
        7,
        14,
        21,
        42
    ],
    "divisor_count": 8,
    "binary": "101010",
    "octal": "52",
    "hex": "2A",
    "roman": "XLII",
    "languages": {
        "english": "forty-two",
        "danish": "toogfyrre"
    },
    "scientific": "4.2 × 10¹",
    "factorial": null
}

A tiny API for integers

Request any integer and get back useful facts and representations — primes, divisors, bases, Roman numerals, English words, and more. Responses are deterministic, cached, and calculated on demand. No API key. No signup.

Try it

Enter an integer and inspect the live JSON response.

Range: -1,000,000,000 … 1,000,000,000

GET /api/42

Response

Loading…

Endpoint documentation

One resource. A few helpers. All responses are JSON.

GET /api/{number}

Return properties and representations for a single integer. Optional query parameter pretty=1 enables indented JSON.

https://numbers.dk/api/42?pretty=1

GET /api/random

Return data for a random integer within the supported range.

https://numbers.dk/api/random

GET /api

Basic API metadata: name, version, and endpoint pointers.

{
  "name": "Numbers API",
  "version": "1.0",
  "endpoint": "/api/{number}"
}

Response fields

Every successful number response includes the following fields.

Field	Type	Notes
number	integer	The requested integer
formatted	string	Thousands-separated display form
previous / next	object\|null	Adjacent integer + API url; null at range edges
absolute	integer	Absolute value
sign	integer	-1, 0, or 1
even / odd	boolean	Parity flags
prime	boolean	True for primes greater than 1
positive / negative / zero	boolean	Sign classification
square / cube	boolean	Perfect power checks
fibonacci / triangular	boolean	Sequence membership (non-negative)
palindrome	boolean	Digit palindrome using absolute value
digit_count / digit_sum	integer	Decimal digit metrics
reversed	integer	Digits reversed, sign preserved
divisors	array	Positive divisors of \|n\|; empty for 0
divisor_count	integer	Length of divisors
binary / octal / hex	string	Base representations; negatives prefixed with -
roman	string\|null	Supported for 1–3999; otherwise null
languages	object	Word forms: english, danish
scientific	string	Scientific notation with Unicode exponents
factorial	integer\|null	Provided for 0–20; otherwise null

HTTP status codes

200— Successful response
422— Invalid or out-of-range number
404— Unknown endpoint
429— Rate limit exceeded

{
  "error": {
    "code": "NUMBER_OUT_OF_RANGE",
    "message": "The number must be between -1000000000 and 1000000000."
  }
}

Rate limits

Anonymous clients are limited to 120 requests per minute per IP. Responses include standard headers:

X-RateLimit-Limit
X-RateLimit-Remaining
Retry-After (on 429)

CORS is enabled for public GET requests, so you can call the API from browser apps.

Code examples

Copy a ready-made request in your language of choice.

cURL

curl -s https://numbers.dk/api/42

JavaScript

const res = await fetch('https://numbers.dk/api/42');
const data = await res.json();
console.log(data);

PHP

$json = file_get_contents('https://numbers.dk/api/42');
$data = json_decode($json, true);
print_r($data);

Python

import urllib.request, json

with urllib.request.urlopen('https://numbers.dk/api/42') as r:
    data = json.load(r)
print(data)

Java

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

var client = HttpClient.newHttpClient();
var request = HttpRequest.newBuilder(URI.create("https://numbers.dk/api/42")).GET().build();
var response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());