1×2+3×4+5×6+……+999×1000=(2²-2)+(4²-4)+(6²-6)+……+(1000²-1000)=(2²+4²+6²+……+1000²)-(2+4+6+……+1000)=4x(1²+2²+3²+……+500²)-(2+4+6+...