Hmm. Certainly a preset formula that takes an input, performs a calculation, and produces an output is a function.
But other things might be functions as well. Being a function doesn't require an algorithm or preset formula, just some way of describing a single output for every input in the domain. A table would be another way to specify a function. Sometimes we know something's a function but we don't know how to calculate it.
So I'm not sure really what they're after in this question, but I'm going to say FALSE.