How do you write an algorithm to generate unique 17 digit number in java ?

Problem statement:
write an algorithm to generate 17 digit unique number.

public class GenerateUniqueRandNums {
    public static void main(String args[]) {
        for (int count = 0; count < 1000000; count++) {
            long unqNum = System.nanoTime();
            System.out.println("unique: " + unqNum* 100);
        }
    }
}
Note: we must create new instance on every single iteration withing a loop, then only it could be, else single instance will get looped over the multiple times.
Output:
unique: 2750731359372300
unique: 2750731485912300
unique: 2750731491573500
unique: 2750731496781900
unique: 2750731501673200
unique: 2750731569698600
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public class GenerateUniqueRandNum {
    public static void main(String args[]) {
        long unqNum = System.nanoTime();
        for (int count = 0; count < 1000000; count++) {
            System.out.println("unique: " + unqNum* 100);
        }
    }

}
Output:
unique: 2946684697352300
unique: 2946684697352300
unique: 2946684697352300
unique: 2946684697352300
unique: 2946684697352300

unique: 2946684697352300
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