We are given:
The compound interest formula for half-yearly compounding is:
\[ A = P \left(1 + \frac{r}{n} \right)^{nt} \]
Substituting values:
\[ 18522 = P \left(1 + \frac{0.10}{2} \right)^{2 \times 1.5} \] \[ 18522 = P (1.05)^3 \] \[ 18522 = P \times 1.157625 \]
Solving for \( P \):
\[ P = \frac{18522}{1.157625} \approx 16000 \]
Final Answer: The initial principal invested was: \[ \boxed{16000} \]