The COUNT function counts the number of cells which contain numbers.

Description from Microsoft here: https://support.office.com/en-US/article/COUNT-function-A59CD7FC-B623-4D93-87A4-D23BF411294C.

Workaround: Implement such a custom function. See Custom Functions help article here: http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions .