ForHosting KIT · Developer Utilities

Pentagonal number calculator

Pentagonal numbers are the figurate sequence that counts dots arranged in nested regular pentagons.

● BetaFree · in your browser

Use it from Web API onlyAPIEmailTelegramApp soon

The closed formula is simple and exact: the n-th pentagonal number equals n times three-n-minus-one, all over two. That identity produces the familiar list 0, 1, 5, 12, 22, 35, 51, and so on for non-negative indexes. This calculator both evaluates P(n) for a chosen index and tests whether an arbitrary non-negative integer is a member of the sequence, using the classical discriminant condition rather than a slow search. Negative indexes are rejected with a clear validation error so callers never confuse this tool with generalized pentagonal numbers used in partition theory. Results are fully deterministic, free in the browser widget, and available as prepaid API items when you wire them into scripts or teaching platforms.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

How do I use this capability?

This capability is currently available through the API. The Web channel is not enabled for it yet.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/math/pentagonal-number

One authenticated POST creates the task; the result comes back by webhook or a signed link. This capability is currently available through the API, not as an interactive Web tool.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/math/pentagonal-number \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"n":5}'

const res = await fetch("https://api.kit.forhosting.com/math/pentagonal-number", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "n": 5
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/math/pentagonal-number",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "n": 5
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/math/pentagonal-number", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"n":5}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"n":5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/math/pentagonal-number", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "n": 5
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "math.pentagonal_number",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`max_n`	10000000
`max_value`	150000000000000

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →