分开写：因为这是个隔项等差数列,就是说奇数列是等差数列,偶数项是等差数列a2m+1=a2m-1+2a2m=a2m+2d都为2 ｛a2m+1｝首项为0 ｛a2m｝首项为3a2m+1=0+2(2m-1)=4m-22m＋1＝n m＝(n-1)/2a2m=3+2(2m-2)=4m-12m=nm=n...