求
SUM(k=1,100){ k*A(101,100-k)}
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除以101!后不就是原题吗?开胃菜上多撒了一把胡椒粉!
-万斤油-
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02/10/2022 postreply
19:35:54
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其和是101阶乘减1。这个全排列与选排列的关系有什么解释没有?
-wxcfan123-
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02/10/2022 postreply
20:47:15
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