Well, it looks like ISOWEEKNUM MS Excel 2013 formula/ function is not supported by Aspose.Cells formula calculation engine. I have tested your scenario/case using a simple Excel file (attached) having ISOWEEKNUM formula applied to A1 cell of the first worksheet in the workbook. When I try to calculate the formula, I got “#NAME?” error.
e.g Sample code:
Workbook wb = new Workbook(@“e:\test2\bk_isoweeknum1.xlsx”);
This is to update you that we have provided the support for the ISOWEEKNUM. We will shortly provide the next build of Aspose.Cells for .NET API here after ensuring the quality and incorporating other enhancements. As soon as the next build is available for your testing, we will notify you here in reference to the ticket CELLSNET-44167.