这道标准数独拥有多个答案，请在圆圈格内填入一个数字，有且仅有一种填法，使其变为仅有唯一解的标准数独。你需要找到这个数字，并解开题目。
This Classic owns more than one solutions. Please write a number in the circle, there's only one choice that can make the puzzle unique. You need to find this number, and solve the puzzle.
标准数独基础上，每种颜色的区域内数字是一组1~6不重复。
Classic rules applied. Additionally, numbers 1~6 cannot repeat in each colored region.
标准数独基础上，数字被分为1、质数、合数三种类型。相同符号表示相同类型，不同符号表示不同类型。
Classic rules applied. Additionally, numbers are divided into three types of 1, prime numbers, and composite numbers. Same symbol means same types, different symbol mean different types.
标准数独基础上，黑点两侧数字为2倍关系，白点两侧数字之差为1。不是所有符合条件的地方都被点标记，1和2之间可能是任意一种标记。
Classic rules applied. Additionally, a black dot means that one of the neighboring digits has the double value of the other digit. A white dot means that the difference of the neighboring digits is exactly one. Dots between 1 and 2 will be white or black.
标准数独基础上，如果箭头格为A，箭头指向的方向上一定有A。
Classic rules applied. Additionally, if the arrow cell is A, then the direction the arrow points must contain A.
标准数独基础上，每个区域内都是从左到右、从上到下的两位数，提示表示这些多位数从小到大进行排序的序号。Classic rules applied. Additionally, digits in each region form multi-digit numbers from left to right、up to down in each zones, and the prompt indicates the sequence number for sorting these multi digit numbers from smallest to largest.
标准数独基础上，提示⑤表示其周围数字之和为5，提示⑥表示其周围数字之和为6。所有和是5或6的情况都被标记了。
Classic rules applied. Additionally, 5 is marked between two digits in adjacent squares with the sum of 5, and 6 likewise. All the adjacent pairs that have a sum of 5 or 6 are marked.
标准数独基础上，涂色格与其任一呈马步的单元格中，不能有相同的数字。
Classic rules applied. Additionally, no two cells that is a knight-step away and contains at least one colored cells can contain the same digit.
标准数独基础上，提示表示其周围两个数的差。
Classic rules applied. Additionally, the clue shows the difference the two numbers around it.
标准数独基础上，3x3方格中的每个格子有序号（六阶是2x3）。如果格内数字和序号一样，那么该格会被涂色标记。所有符合条件的情况被全部标记。
Classic rules applied. Additionally, each of the digit describes (correctly or not) the position of it's cell in 3x3 square (2x3 in 6x6). All correctly described cells are highlighted.
