求第1500个只有2,3,5因子的数。数是从小到大排列，第一个数是1,1=2^0*3^0*5^0。 要求用C/C++实现。时间复杂度不超过O( )。-No. 1500 for only a few factors 2,3,5. A few are from small to large order, the first number are 1,1 = 2 ^ 0* 3 ^ 0* 5 ^ 0. Asked to use C/C++ implementation. Time complexity less than O ().