C Sharp :: Count And Delete In File

So I have this program which read single text file and write in other. Basically read every line then write to another file "this number is n times here + numbers".

How to modify this to store only 1 time the number in second file. What I mean is not like now:

Now output is:

Count of matching numbers in this group: 7
Numbers:
01070400
01070400
01070400
01070400
01070400
01070400
01070400

Is better to be:
Count of matching numbers in this group: 7
Number:
01070400  

Code that I use is:
            string path = "text.txt";  
            var result = (File.ReadLines(path)).OrderBy(x => x).GroupBy(x => x);  
            using (var writer = new StreamWriter("test1.txt")) {
                foreach (var item in result) {
                    string outGrp = String.Format("Count of matching numbers in this group: {0}", item.Count());
             
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