20x125x25x64=（20x25）x8x（8x125）=500x8x1000=4000000
原式=20x125x8x25x8=20x1000x200=4000000
20×125×25×4×8×4＝20×4×125×8×25×4＝8000000
20拆成4乘以。64拆成8乘以8
5*4*25*8*8*125
