Checking duplicants in LINQ

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LINQ

Hi,

I have a query which will give the duplicate of the number, but when i entered Upper case and lower case number it was not taking as duplicate.

Number: TEST1
Number: test1

my linq query:

var Duplicatenumber = from a in Listnum
                                  join b in serialmaster on a.ID equals b.list_Id
                                  select new
                                  {
                                      Line = a.LineNumber,
                                      SAPLine = a.SAPLine,
                                      Code= a.Code,
                                      Description = a.Description,
                                      Number = b.number,
                                      NumberID = b.NumberID,
                                      CodeID = a.ID

                                  };
        // Code Change for eliminate the empty values
            var ExactDuplicate = from a in Duplicatenumber 
                                 where !string.IsNullOrWhiteSpace(a.Number)
                                 group a by new { a.Number } into g
                                 where g.Count() > 1
                                 select new
                                 {
                                     g.Key.Number

                                 };