因为 1/4a^4+1/2a^3+1/4a^2=1/4(a^4+2a^3+a^2)=1/4*a^2*(a^2+2a+1)=1/4*a^2*(a+1)^2=1/4*[(a(a+1)]^2=[1/2a(a+1)]^2注意到a是整数时,a与a+1是两个连续的整数,连续整数中必有一个是偶数,所以1/2a(a+1)必为整数.因此上...