It's an approximation. The sentence is perhaps confusing since it might imply that n! ≈ 10^n but that's not the case, the article uses 24 and 25 as the cut poin

It's an approximation. The sentence is perhaps confusing since it might imply that n! ≈ 10^n but that's not the case, the article uses 24 and 25 as the cut point where the approximation is true. The linked post is more informative: https://www.johndcook.com/blog/2023/06/22/mentally-approximating-factorials/ https://www.johndcook.com/blog/2023/06/22/mentally-approxima...