这个数列的通项an = n(n+1)即 an = n^2 + nn(n+1)(2n+1)其中1^2 + 2^2 + 3^2 + ...+ n^2 = --------------6n(n+1)1+2+3+...+n = ------------2所以1X2+2X3+3X4+.NX(N+1) N(N+1)(2N+1) N(N+1)= ---------------- + --...