根据题意得:当选1时,k+2,2k+3…k2∴得出k2=(k-1)k+k∴1+k+2+2k+3+…+(k-1)k+k= k(k2+1) 2 ∴做了k次后,所取出的k个数的和是 k(k2+1) 2 = k3+k 2 .故答案为: k3+k 2 .