No. They just have to satisfy the vectors axioms (greatly simplifying, you can add vectors together and multiply them by scalars , and they behave as you would expect - associative, commutative, distributive, etc as appropriate.)

So, in this regard, functions can be vectors, if you define addition to be pointwise addition. For example, consider the set of continuous functions on the unit interval [0, 1]. Add two together and you get another continuous function on the unit interval, multiply by a scalar and you get another continuous function on the unit interval, etc.

In this sense, vectors can always be written as lists of numbers, but no, they don't have to be this in general. For example, you could have a vector space of smooth functions. It's infinite dimensional, and its elements (its vectors) are functions, not tuples of numbers.