Nice! One suggestion: allow the viewer to input a number to view directly its factorization instead of having to wait until that number is reached - although it may not be efficient if the program caches the prime numbers and factorizations. Which brings me to my second question: is the code available somewhere? The website uses a minified version of the js code. Not the most pleasant to understand the algorithm.
> although it may not be efficient if the program caches the prime numbers and factorisations
If you watched this website non-stop for a whole year, it would still only take a thousandth of a second or so to factorise the highest number you'd reach, from scratch. Integer factorisation is only time consuming when the numbers are really really big.
