[Solved] Which references am I missing?

You seem to be confusing the ExcelPackage project and the EPPlus project. I can see how as they share namespaces and class names (I don’t know the history of either to know if they’re related or not).

You have a reference to the ExcelPackage dll in your example. The ExcelWorksheet class there doesn’t have a Cells property; instead it has a Cell method.

The ExcelWorksheet class in EPPlus does have a Cells property that returns an ExcelRange. The ExcelRange in turn has an indexer that looks like this which would allow the code you have to work:

public ExcelRange this[int Row, int Col]

To get your code to work using ExcelPackage you will need to change to using the method:

worksheet.Cell(row, col).Value = (row * col).ToString();

Note that the Value property is a string so I’m calling ToString()

If you would prefer to keep your code as is you could remove the reference to ExcelPackage and add a reference to EPPlus instead (which is available on Nuget). I have no idea which is better but running your code against both (with the above fix for the ExcelPackage version) gives me a warning when loading the file created by ExcelPackage in Excel but it doesn’t for the one created via EPPlus.