设数列的第n项为an则an-a(n-1)=n-1a2-a1=1a3-a2=2a4-a3=3a5-a4=4…………an-a(n-1)=n-1上面几式相加得an-a1=1+2+3+ …+(n-1)=(n-1)n/2把a1=1代入得an=(n-1)n/2+1所以a100=99×100/2+1=99×50+1故a100÷5=(99×50+1)...