2014!=2014X2013X2012X...X12015!=2015X2014X2013X...X1(2015!)/(2014!)=(2015X2014X...X1)/(2014X2013X...X1)=2015
2014!分之2015!=(2014x2013x2012x……×2x1)分之(2015×2014x2013x2012x……×2x1)=2015