13. (15 points) Let each Chinese character in the four idioms “一家之言”、“言扬行举”、“举世皆知”、“知行合一” represent one of 11 consecutive non-zero natural numbers, with the same character representing the same number and different characters representing different numbers. If the sum of the numbers represented by the four characters in each idiom is 21, what is the largest number that “行” can represent?

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The translation is provided while maintaining the original text's format and line breaks.
【Analysis】First, find the frequency of these characters, paying attention to the number of repetitions, then represent these 11 numbers, and based on the sum of the numbers being 21, the sum of 4 numbers is 84. Using the relationship that when the sum of numbers is constant, one number is larger while the other is smaller, find the maximum value.

【Solution】Solution: Upon observation, it is not difficult to find that “一”, “言”, “举”, “知”, “行” each appear twice, while the other Chinese characters appear only once. Let the numbers represented by these five characters be $a, b, c, d, e$ (all positive integers), and let the 11 consecutive natural numbers be $(x+1),(x+2), \cdots(x+11)$,

then $(x+1)+(x+2)+\cdots+(x+11)+a+b+c+d+e=21 \times 4$,
which simplifies to $11 x+a+b+c+d+e=18$, so $x=0$,
and when $a+b+c+d+e=1+2+3+4=10$, $e$ is maximized at 8,
the 11 numbers are from 1 to 11. We can construct “一家之言”, “言扬行举”, “举世皆知”, “知行合一” as “$3,5,11,2$”, “$2,10,8,1$”, “$1,9,7,4$”, “$4,8,6,3$”.

In summary: “行” can represent the number 8 at most.