2,-6,12,-20,30,-42,……第n个数是
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2,-6,12,-20,30,-42,……第n个数是
2,-6,12,-20,30,-42,……第n个数是
2,-6,12,-20,30,-42,……第n个数是
n为奇数时,an=-(n²+n+2)
n为偶数时,an=n²+n+2
也可以概括成an=-(n²+n+2 )×(-1)的n次方
规律是:
2,-6,12,-20,30,-42,……第n个数是
2,-6,12,-20,30,-42,……第n个数是
2,-6,12,-20,30,-42,……第n个数是
n为奇数时,an=-(n²+n+2)
n为偶数时,an=n²+n+2
也可以概括成an=-(n²+n+2 )×(-1)的n次方
规律是: