1\4\10\20\35\56\84\120\165\220……请帮忙拟出排列规律?
人气：210 ℃ 时间：2019-08-21 15:22:15
解答
a=1=C(3,3)
a=4=C(4,3)
a=10=C(5,3)
a=20=C(6,3)
a=35=C(7,3)
a=56=C(8,3)
a=84=C(9,3)
a=120=C(10,3)
所以规律是组合数C(n+2,3)=(n+2)(n+1)n/3!
即a=n(n+1)(n+2)/6
我复制的
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