Find the smallest power of 2 (`2^k`) that is greater than or equal to `n`, then subtract 1 to get the candidate number `(2^k) - 1`.

If the candidate number is less than `n`, increment `k` and repeat until the candidate is >= `n`.

Alternatively, compute the number of bits required to represent `n` (e.g., `bit_length = n.bit_length()`), then check if `(1 << bit_length) - 1` is >= `n`. If not, use `(1 << (bit_length + 1)) - 1`.