 If we use a position system to represent the number n then the process of identifying factors of n by trial and error will take a deterministic computer program at most n trials which gives a computation time exponential in the length of the representation of the number which is \(\lceil \log n \rceil \). Factorization by trial and error of a relatively simple number, of, say, two hundred digits, which codes a rather small message, could easily take a computer of the size of our whole universe longer than the time passed since the big bang. So, although theoretically feasible, such algorithms are completely unpractical. 