TAOCP 1.2.2 Exercise 20

Yes.

Section 1.2.2: Numbers, Powers, and Logarithms

Exercise 20. [10] Is there any simple relation between $\log_{10} 2$ and $\log_2 10$?

Verified: yes
Solve time: 36s


Yes. By the change-of-base formula (14),

$$ \log_2 10=\frac{\log_{10}10}{\log_{10}2}. $$

Since $\log_{10}10=1$, this becomes

$$ \log_2 10=\frac{1}{\log_{10}2}. $$

Therefore the two quantities are reciprocals:

$$ (\log_{10}2)(\log_2 10)=1. $$

Using Eq. (10),

$$ \log_{10}2=0.30102999\ldots, $$

hence

$$ \log_2 10=\frac{1}{0.30102999\ldots}=3.32192809\ldots. $$

Thus

$$ \boxed{\log_2 10=\frac{1}{\log_{10}2}}. $$