It should be the sum of n n, equal to the square of n; N is different from countless ones. Even if n is extremely large, it can only be said that n approaches infinity, which is why there is a symbol "∞" in mathematics, which can be expressed by n→∞, but not by n=∞. So we can only say N plus N, that is, N+N+...+N (* * with N) =nXn=n? .