Solution (source code)

= Solution

\b[True.] The <logarithm> identity gives
$$
\ln(e^n+n)-n=\ln(1+ne^{-n}).
$$
For $n\geq1$, $e^n\geq n$, so $0\leq ne^{-n}\leq1$. By <monotonicity> of the <natural logarithm>, the expression lies between $0$ and $\ln2$. It is therefore $O(1)$ in <Big O notation>.