How to create a screensaver in Core C#

This program was written as an old style screensaver as a part of a training course. The screen saver is a simple program which uses random numbers to display dots on screen in different colors. It also uses a simple logic to keep removing dots by overwriting them with blank spaces, so that the screen does not fill up. There is a for loop to slow down the appearance of dots, i.e., stars. This code is not the last code, suggestions and improvements are welcome. Note: The % operator is used to generate actual randomness on screen, using many if-elses. Only later was it discovered that one can also pass a seed number for effective random values. Note: This program generates only 10000 times. One can also pass a command line argument to run the loop indefinitely and prompt user to press Control+c to exit from the program.

using System;
class set_cursor2
{ 
int lastnum;
 
private int RandomNumber(int min, int max)
{
   Random random = new Random();
   lastnum = random.Next(min, max); 
 
   if (lastnum%3 == 0 || lastnum%4==0 )
   {
      lastnum = random.Next(min, max); 
   }
 
   if (lastnum%5 == 0 || lastnum%6==0 || lastnum%7==0 ) 
   {
      lastnum = random.Next(min, max); 
   }
 
   return lastnum;
}
 
static void Main(string[] args)
{
   set_cursor2 obj = new set_cursor2();
   int lastrow,lastcol;
   int i,j,t;
   Console.ResetColor();
   Console.Clear();
   Console.SetWindowSize(100,50);
   Console.BufferHeight = 500;
   Console.BufferWidth = 200;
   Console.CursorSize = 50;
   Console.CursorVisible = true;
 
   i = 1;
   do
   {   	
      j=  obj.RandomNumber(1,99);
      Console.CursorLeft = j;
      lastcol = j;
      j=  obj.RandomNumber(1,49);
      lastrow = j;
      Console.CursorTop = j;
      if (i%3 == 0)
	Console.ForegroundColor = ConsoleColor.White;
      else if (i%4 == 0)
         Console.ForegroundColor = ConsoleColor.Cyan;
      else
         Console.ForegroundColor = ConsoleColor.DarkBlue;
 
      if ((i+j) % 2 == 0 || (i+j) % 3 == 0  || (i+j) % 5 == 0)	
         Console.WriteLine(" ");
      else
         Console.WriteLine(".");
 
//    Console.WriteLine(". {0} {1}",lastrow,lastcol);
      for(t=0;t<19999999;t++);
      i++;
   }
 
   while (i<=10000);	
   Console.WriteLine("\n\n Finish");
   Console.ReadLine();
}
}

Anyone can use the color codes to change the layout of the screen. The following are some popular color codes:

Color	Description
Black	The color black.
Blue	The color blue.
Cyan	The color cyan (blue-green).
DarkBlue	The color dark blue.
DarkCyan	The color dark cyan (dark blue-green).
DarkGray	The color dark gray.
DarkGreen	The color dark green.
DarkMagenta	The color dark magenta (dark purplish-red).
DarkRed	The color dark red.
DarkYellow	The color dark yellow (ochre).
Gray	The color gray.
Green	The color green.
Magenta	The color magenta (purplish-red).
Red	The color red.
White	The color white.
Yellow	The color yellow.