24. Find the sum of all even factors of 1152 .
(ans. 3302.
$1152=2^{7} 3^{2}$. The even factors of 1152 are each of the form $2^{k} 3^{l}, 1 \leq$ $k \leq 7,0 \leq l \leq 2$. Hence the sum can be written as $\left(2+2^{2}+\cdots+\right.$ $\left.\left.2^{7}\right)\left(1+3+3^{2}\right)=2 \frac{\left(1-2^{7}\right)}{1-2} \cdot 13=3302\right)$