Pascal Triangle implementation in C#
First: The Pascal Triangle will grow very rapidly. And rows=100, your maximum value is 1.27388061294904e+28. Yes, that's right it will overflow int, uint, long, and ulong within 100 rows. Check it out on interactive pascal triangle site
The only suggestion is Numerics.BigInteger where there is no upperbound.

Second: Why are you using List&lt;List&lt;int&gt;&gt;? You can use a jagged array, which is much shorter: int[][], and effectively does the same. You just need to initialize them ahead with their size

var triangle = new int[rows][];
for(int i = 0; i&lt;rows;i++){triangle[i] = new int[i+1];}


Third: if you know the first and last element is always a 1, then the if-statement for the first 2 rows is redundant

// This part is redundant, you already check if the first/last element is 1
if (x == 0 || x == 1)
{
    result.Add(Enumerable.Repeat(1, x + 1).ToList());
}


So with all the improvements, you code would be shorter and could handle much more rows. As a bonus I removed the dependency on system.linq. It could look like this:

public static BigInteger[][] GetPascalTriangleImproved(int rows)
    {
        BigInteger[][] result = new BigInteger[rows+1][];
        for (int x = 0; x &lt; rows; x++)
        {
            result[x] = new BigInteger[x + 1];
            result[x][0] = 1; // first element is ALWAYS 1

            for (int x1 = 1; x1 &lt;= x; x1++)
            {
                // last element is always 1 (just like the first)
                if (x1 == x) { result[x][x] = 1; continue; }

                // in all other cases, just add the 2 digits in the upper row
                result[x][x1] = result[x - 1][x1 - 1] + result[x - 1][x1];
            }                
        }
        return result;
    }