Theorem T49 nnen−1≤n!≤nn+1en−1\frac{n^n}{e^{n-1}} \leq n! \leq \frac{n^{n+1}}{e^{n-1}} en−1nn≤n!≤en−1nn+1 for integer n≥1n \geq 1n≥1. number-e notation-factorial