c# , Could anyone understand why it didn't pass test 1?

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {

    static void Main(String[] args) {
        int t = Convert.ToInt32(Console.ReadLine());
        for(int a0 = 0; a0 < t; a0++){
            int n = Convert.ToInt32(Console.ReadLine());
            int sonuc = Fonk(n);
            Console.WriteLine(sonuc);
        }
    }
    static int Fonk(int n){
        int sum = 0;
        int sum2 = 0;
        int sonuc = 0;
        
        for(int i = 1; i <= n; i++){
            sum += i;
            sum2 += i * i;
        }
        
        sonuc = sum * sum - sum2;
        return sonuc;
    }
}

JAVA 8

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int t = in.nextInt();
    long n[] = new long[t];
    long count[]= new long[10000];
    long result[] = new long[t];
    double result1=0;
    double result2=0;

    for(int i=0; i<t; i++){
        n[i] = in.nextInt();
        for(int j=0; j<n[i]; j++) {
            count[i]+=j+1;
            result2+=Math.pow(j+1,2);
        }
        result1=Math.pow(count[i], 2);
        result[i]=((long)(result1-result2));
        result1=0; result2=0;
    }

    for(int i=0; i<t; i++) {
        System.out.println(result[i]);
    }
    in.close();
}

hey can someone help me out with this problem? im new to competitive programming and my friend sent me this. he wants me to solve it but as i said, im still new so can yall teach me? here is the problem https://www.hackerrank.com/newbie-challenge

long n1=(n*(n+1)/2); long n2=(n*(n+1)*(2*n+1))/6; by using this formula it give wrong out put 10000 by using normal traditonl method using loop gives correct answer is there any one discuss on this .

Python3

for _ in range(int(input())):
    x = int(input())
    s1 =0
    s2 =0
    for i in range(0,x+1):
        s1 += i*i
    for i in range(0,x+1):
        s2 += i
    s2 = pow(s2,2)
    print(s2-s1)