please give me a formula to find for example n! contain how many characters?

n= 10
result = 7
You can find the number of digits without calculating the actual factorial by using Stirling's approximation.

An approximation of n! is
sqrt(2*pi*n) * (n/e)^n

Take the log to base 10 and add 1 to find the number of decimal digits.
0.5*log10(2*pi*n) + n*log10(n/e) + 1
thank you very much
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