21. PS 已知三位数n表示为2^x 3^y 5^z, 前面三个数分别为百位,十位和个位,f(x)是n的所有因数的个数,已知f(m)=9f(v), 问m-v是多少 楼主认为是80 因为m的十位是3^2=9,v的十位是3^0=1 ------------------------------------------------------------------------------------------------------------ GWD18-Q6: The function f is defined for each positive three-digit integer n by f(n) = 2x 3y 5z, where x, y and z are the hundreds, tens, and units digits of n, respectively. If m and v are three-digit positive integers such that f(m) = 9 f(v), then m - v =