质数 Prime

标准数独基础上，灰色区域内的多位数是质数（从左到右，从上到下）。质数是一个数学术语，它没有除了1和它本身之外的其余因数。

Classic rules applied, numbers are multi-digit prime number in grey zones with order (left → right, up → down). Prime number is a Mathmatical Term, prime numbers has no other factors, without 1 and itself.

◆解题时，我们一般先考虑数字的末位。例如六阶质数数独的末位只能是1或者3，而九阶质数数独的末位只能是1、3、7、9。

It's a normal way to consider about the last digit. A prime number in 6x6 puzzles must end with 1 or 3, and 1、3、7、9 in 9x9 puzzles.

练习 Practice

① 六阶质数数独中，一个两位数质数以3结尾，十位数不可能是______。

In Prime 6x6, if a 2-digit prime end by 3, then the tens number cannot be ______.

② 九阶质数数独中，一个两位数质数包含了数字9，它可能是______。

In Prime 9x9, if a 2-digit prime contains 9, it may be ______.

③ 找到问号格的答案 Find out the ？cells.

答案 Answer

① 3 and 6 ② 19、29、59、79、89、97 ③ C2=3.