Collatz Calculator
Trace the Collatz sequence for any starting number.
What is Collatz?
The Collatz rule is simple: an even number halves, an odd number triples and adds one, and the conjecture — open since 1937 — is that every starting value eventually reaches 1. The interesting number is usually the peak: 27 takes 111 steps and climbs to 9,232 first, which is why a small input can produce a long trace.
How it works
The sequence is traced term by term, counting steps and tracking the largest value reached. Every starting value ever tested does reach 1 — checked by computer to about 2⁶⁸ — but that is evidence, not proof, so the engine stops after 10,000 steps and says so rather than looping forever: no trace has ever needed that many, and none is known to need them.
- 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.