(2000-1)*2000 *(2000+1)*(2000+2)+1
=2000 *(2000+1) * (2000-1)*(2000+2)+1
=(2000²+2000) *(2000²+2000-2)+1
=(2000²+2000) -2*(2000²+2000)+1
=(2000²+2000 -1)²
于是开根号得到2000²+2000 -1
即4001999
2000*(2000-1)*(2000+1)*(2000+2)+1
=2000*(4000000-1)*(2000+2)+1
=(4000000+4000)*(4000000-1)+1
=16000000000000+16000000000-4000000-4000+1
=16015995996001