Longest Repeated Pattern in a List

The goal is to find the longest repeating pattern, given a list. Being a bit new to C# I found a similar program but referring to Strings here:

https://www.javatpoint.com/program-to-find-longest-repeating-sequence-in-a-string

So far my code looks like this:

using System;     
using System.Collections.Generic;  
public class Solution
{  
    //Checks for the largest common prefix  
    public static List<int> lcp(List<int> s, List<int> t){  
        int n = Math.Min(s.Count,t.Count);  
        for(int i = 0; i < n; i++){  
            if(s[i] != t[i]){  
                return s.GetRange(0,i);  
            } 
        }  
        return s.GetRange(0,n);
    }  
      
    public static void Main()  
    {  
        int[] use = {1,2,3,4,5,1,2};
        List<int> list = new List<int>(use);
        //List<int> sublist = list.GetRange(1, 4);
        
        List<int> lrs = new List<int>();  
        int n = list.Count;  
        for(int i = 0; i < n; i++){
           for(int j = i+1; j < n-i; j++){  
                //Checks for the largest common factors in every substring 
               List<int> x = new List<int> ();
               
               x = lcp(list.GetRange(i,list.Count-1),list.GetRange(j,list.Count-1));

                //If the current prefix is greater than previous one   
                //then it takes the current one as longest repeating sequence  
               if(x.Count > lrs.Count) lrs=x;    
            }  
        }  
       Console.WriteLine("Longest repeating sequence: "+lrs);  
    }  
}  

However I'm getting the following error and don't know how to fix it. I have messed around a bit with the indexes but can't figure it out:

Unhandled Exception:
System.ArgumentException: index and count exceed length of list
  at System.Collections.Generic.List`1[System.Int32].CheckRange (Int32 idx, Int32 count) [0x00000] in <filename unknown>:0 
  at System.Collections.Generic.List`1[System.Int32].GetRange (Int32 index, Int32 count) [0x00000] in <filename unknown>:0 
  at Solution.Main () [0x00000] in <filename unknown>:0 
[ERROR] FATAL UNHANDLED EXCEPTION: System.ArgumentException: index and count exceed length of list
  at System.Collections.Generic.List`1[System.Int32].CheckRange (Int32 idx, Int32 count) [0x00000] in <filename unknown>:0 
  at System.Collections.Generic.List`1[System.Int32].GetRange (Int32 index, Int32 count) [0x00000] in <filename unknown>:0 
  at Solution.Main () [0x00000] in <filename unknown>:0