136 - Ugly Numbers

Ugly Numbers

Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence

1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, ...

shows the first 11 ugly numbers. By convention, 1 is included.

Write a program to find and print the 1500'th ugly number.

Input and Output

There is noinput to this program. Output should consist of a single line asshown below, with <number> replaced by the number computed.

Sample output

The 1500'th ugly number is <number>.

#include<stdio.h>
int main(void)
{
int un[1505]={0};
int m2=0,m3=0,m5=0,i,t;
un[0]=1;
for(i=1;i<1500;i++)
{
if(2*un[m2]>3*un[m3])
t=un[m3]*3;
else
t=un[m2]*2;
if(t>un[m5]*5)
t=un[m5]*5;

if(t == 2*un[m2]) m2++;
if(t == 3*un[m3]) m3++;
if(t == 5*un[m5]) m5++;

un[i]=t;
}
printf("The 1500'th ugly number is %d.\n",un[1499]);
return 0;
}