You want this code:
for(int j = 2; j <= 4; j++)
{
for(int i = 1; i <= 20; i++)
{
if (i % j == 0)
Console.Write("{0} ", i);
}
Console.WriteLine();
}
Think why this is a correct and elegant way to do your task.
solved For loop to print numbers from 1-20 divisible by 2, second line for divisble 3third is for divisble by 4?