I would go further and suggest that /usr/bin/factor is not something that should be in coreutils, and that OSX/BSD is far more sensible than GNU in excluding it. It just ends up polluting /usr/bin with functionality that would make more sense in a basic calculator like "bc" (which I curse out every time I start it because its so much easier to do basic arithmetic in python, ruby, R or octave).
If you look at what else is in coreutils factor seems completely out of place. There is not a single other tool in coreutils to do basic arithmetic. Where is there a /usr/bin/factor but not a /usr/bin/factorial, /usr/bin/exponent, /usr/bin/log or for that matter a /usr/bin/prime or /usr/bin/primes. In fact a good multi-function random tool (to generate random numbers or strings) would seem to be a far far far more useful thing to add to coreutils than "factor."
I'm really curious what considerations lead to "factor" being included into coreutils, is there an init script that really needs to factor a number before it can continue?
I don't mean this as a criticism of the developers of bc or coreutils or of GNU in general. Tools like "bc" were advanced and useful for their day. Thankful we have better alternatives for many use cases, and with 8 cores and 16GB of RAM I'm happy to waste a bit of each to get a more use friendly tool to do basic arithmetic and really don't need "bc" or "factor" anymore.