求
SUM(k=1,100){ k*A(101,100-k)}
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除以101!後不就是原題嗎?開胃菜上多撒了一把胡椒粉!
-萬斤油-
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02/10/2022 postreply
19:35:54
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其和是101階乘減1。這個全排列與選排列的關係有什麽解釋沒有?
-wxcfan123-
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02/10/2022 postreply
20:47:15
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