求
SUM(k=1,100){ k*A(101,100-k)}
• 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- ♂ (0 bytes) () 02/10/2022 postreply 19:35:54
• 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- ♂ (0 bytes) () 02/10/2022 postreply 20:47:15
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