C# Beginner Question -- How to call a function from a separate script in multiple other scripts

This may be an obvious problem that is just not clicking to me and I've been googling for the last hour or two and has of yet, not been able to find a solution to my problem.

To start off, I'm creating an idle game and within this game, numbers can become quite large so I created a script that runs and input through a series of if-statements to determine whether it needs to be abbreviated and/or what abbreviation it needs dependent on how long the number itself is.

This script works find when testing from within the script itself. However, when I try to call it from another script in order to make different numbers auto-abbreviate, I continuously get a null exception stating the object reference is not set to an instance of the object. Being new to Unity and having not programmed in quite some time, I have absolutely no idea why this happens.

The following code is the script that converts the numbers.

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class LargeNumberConverter : MonoBehaviour {
 
     string output = "";
 
     public string Convert(double number) {
         if (number >= 1e+123) {
             number /= 1e+123;
             output = number.ToString ("###.000 'dd'");
             return output;
         } else if (number >= 1e+120) {
             number /= 1e+120;
             output = number.ToString ("###.000 'cc'");
             return output;
         // (...omitted for length...)
         } else
             return output;
     }
 }

The following script is one example of trying and failing to call the script into another script.

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class Click : MonoBehaviour {
 
     public Text clickPower;
     public Text followerDisplay;
     public float followers = 0.00f;
     public int followersPerClick = 0;
     public LargeNumberConverter lnc;
 
     void Update() {
         followerDisplay.text = "Followers: " + lnc.Convert((double)followers);
         clickPower.text = "Idol Power: " + lnc.Convert((double)followersPerClick);
     }
 
     public void Clicked() {
         followers += followersPerClick;
     }
 }

I would appreciate the help of anyone willing as I'd like to get passed this as soon as possible.