[问题] 一题组合 /o/

楼主: TassTW (為文載道尊於勢)   2005-01-02 23:19:58
k为正整数
k 2k-1 i-2 2k-i-1 2k-2
Σ C i-1 ×(i) ×(2k-i+1) = (2k+1)
i= 1
ex:
k=2时有 1*1*4 + 3*1*3 = 5^2

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