试一下,n(n+1)/2 ?
所有跟帖:
• 厉害,是的。怎么推导的? -math357- ♂ (0 bytes) () 02/15/2022 postreply 08:06:17
• 没推导,就先试试前几个数,猜一下公式,最后证明一下 -三兔之家- ♀ (0 bytes) () 02/15/2022 postreply 08:14:34
• 厉害,是的。怎么推导的? -math357- ♂ (0 bytes) () 02/15/2022 postreply 08:06:17
• 没推导,就先试试前几个数,猜一下公式,最后证明一下 -三兔之家- ♀ (0 bytes) () 02/15/2022 postreply 08:14:34
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