If the difference is one, then one of the two is

來源: 於 2010-04-01 11:47:04 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

an even number. If it's 2, then the other one is 1 or 3. If it's not 2, then it can be divided by 2. Therefore, not a prime. So it must be 2.