因为(2n)!=[1*3*5*...*(2n-1)]*[2*4*6*...(2n)] =[1*3*5*...*(2n-1)]*[(2*1)*(2*2)*(2*3)*...(2*n)]=[1*3*5*...*(2n-1)]*[2^n*(1*2*3*...*n)]=[1*3*5*...*(2n-1)]*(2^n*n!)所以 (2n)!/(2^n*n!)=1*3*5*...*(2n-1)....