>>574
�@
A(2k-1) - A(2k)
= (1/2)((2k-1)-1)(2k-1) - (1/2)(2k -1)2k
= -(2k-1)
�A A(1) = 1 , (N+1) A(n+1) = N A(n)てこと?
N A(n) = (N-1) A(n-1) = ・・・・ = 1・A(1) = 1
∴A(n)=1/N