In other words, an icon showing whatever-wall status, submitter can add an alternate link, etc.

If a number is not prime, then it is the product of at least two numbers smaller than itself.

If any of them are larger than its square root, all others must be smaller, or their product would be larger than the candidate prime.

Ergo, just check that the candidate is not evenly divisible by any number equal or lower than its square root.

This reasoning holds, independent of scale.

QED. Check mate. Shazam.