Those are very rough approximations: 24! is about 60% of 10^24 and 25! is about 155% of 10^25. It's simpler to remember that 24.5! ≈ 10^24.5 (accurate to withi

Those are very rough approximations: 24! is about 60% of 10^24 and 25! is about 155% of 10^25. It's simpler to remember that 24.5! ≈ 10^24.5 (accurate to within +/- 3%; see https://www.wolframalpha.com/input?i=solve+x%21+%3D+10%5Ex https://www.wolframalpha.com/input?i=solve+x%21+%3D+10%5Ex)