Question

Find the sum of divisors of $18$

Answer 1

We have, $18=2^1\times 3^2$

$\sigma \left(N\right)=\left(\frac{2^{1+1}-1}{2-1}\right)\left(\frac{3^{2+1}-1}{3-1}\right)$

$=3\times \frac{26}{2}=39$