41. Given the four-digit number $\overline{4 a b 5}=5 \times x \times 11 \times y$, where $x, y$ are both prime numbers, then the number of such four-digit numbers is $\qquad$, and the largest one is $\qquad$
Answer: $3 ; 4785$.

Solution: Since
$\overline{4 a b 5}$ is a four-digit number,

we have
$$
\overline{4 a b 5}<5000 \text {, }
$$

which means
$$
5 \times x \times 11 \times y<5000 \text {, }
$$

thus, one of $x, y$ must be less than 10.
Assume $y<10$, then $y=3$ or 5, or 7.
When $y=3$, $\overline{4 a b 5}=5 \times x \times 11 \times 3=165 x$,
from $4005 \leq 165 x \leq 4995$, we get $25 \leq x \leq 30$.

Since $x$ is a prime number,

$x=29$, at this point the four-digit number is $5 \times 29 \times 11 \times 3=4785$.
Similarly, when $y=5$, $x=17$, at this point the four-digit number is $5 \times 17 \times 11 \times 5=4675$; similarly, when $y=7$, $x=11$, at this point the four-digit number is $5 \times 11 \times 11 \times 7=4235$. In summary, there are 3 four-digit numbers that meet the conditions, the largest of which is 4785.