Happy Number Checker
Check whether a number is happy, with the chain shown.
What is Happy Numbers?
A happy number reaches 1 when replaced repeatedly by the sum of the squares of its digits: 19 → 82 → 68 → 100 → 1. An unhappy number does not wander forever — it always lands in the same cycle, 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20, which is why a sad number's answer can name the loop it fell into rather than a bare no.
How it works
Each step sums the squares of the digits, and the values visited are kept in a set so the first repeat is caught the moment it appears: reaching 1 means happy, and repeating means the loop is known. The first step is written out with its digit squares (19 → 1² + 9² = 82) because the rule is the thing being shown, and the whole chain is listed so it can be followed by hand.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.