19. (10th grade) Simplify $1!1+2!2+3!3+\ldots+n!n$.

将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。
19. Transform each term of the sum according to the following rule $k!k=(k+1)!-k!$, then $1!1+2!2+\cdots+n!n=2!-1!+3!-2!+\cdots+(n+1)!-n!$

Answer: $1!1+2!2+\ldots+n!n=(n+1)!-1$.