Random 3 Digit Letter No Duplicate

I need to know how many four letter strings I can generate that begin with the letter "v". Now I had been testing many ways to do this but anm stuck. I can generate a single line up only a certain amount. I need it to continue till it reaches the max number. So since it needs to always start with V i eliminated the need for four and only a 3 letter string.

package javaapplication4;
import java.util.Random;
public class JavaApplication4 {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Random r = new Random();
int c = r.nextInt(26)+ (byte)'a';

[code]...