You’ve seen how numbers are hidden when they are entered in password fields. You can do the same thing in Excel. The number will still be in the cell, but it is shown as the character you define. For example, the custom numeric format,
Fills the cell with the letter N. You can still use the content of that cell for calculations, but the calculation’s results will also be disguised. To see the calculation’s result you will have to apply a normal numeric format to the calculation’s cell.