  The set of primitive recursive functions is a huge class of computable functions. In fact, they can be characterized as the set of functions computable in time that is some primitive recursive function of \(n\), where \(n\) is the length of the input. For example, since \(H(n,n)\) is a primitive recursive function, the primitive recursive functions include all of TIME[\(H(n,n)\)]. (See the next section for a discussion of computational complexity, including TIME.) Thus, the primitive recursive functions include all functions that are feasibly computable by any conceivable measure of feasible, and much beyond that.