12. (5 points) If $A$ is a prime number, and $A-4, A-6, A-12, A-18$ are also prime numbers, then $A=$
【Solution】Solution: According to the problem, we know: $A-18$ is a prime number, so $A>18, A-6>12, A-4>14$. Enumerating the prime numbers that differ by 2 and meet the conditions, we have $(17,19),(29,31),(41,43),(59,61),(71,73)$, a total of five pairs. $\because A-4$ and $A$ differ by 4, adding 4 to the larger number in the pairs that meet the condition. $\therefore 19+4=23$ (meets the condition), $31+4=35$ (does not meet), $43+4=47$ (meets the condition), $61+4=65$ (does not meet), $73+4=77$ (does not meet). $\because A-6$ and $A-12$ differ by 6, the smaller number minus 6 is still a prime number. $17-6=11$ (meets the condition), $41-6=35$ (does not meet).

At the same time, $A-18$ is also a prime number, differing by 6 from $A-12, 11-6=5$ (meets the condition).
$$
\therefore A, A-4, A-6, A-12, A-18 \text { are } 23,19,17,11,5 \text {. }
$$

Therefore, the answer is: 23.