Getting a count of the number of worksheets in a spreadsheet
Follow the instructions on this site, in order to get a count of the number of worksheets in a spreadsheet.
Go to Formulas tab and in the 'Defined Names' section select 'Define Name'
In the dialog box that appears use the name 'countsheets' and then enter the formula =GET.WORKBOOK(1)&T(NOW()) in the 'Refers to' box.
Now you can just enter the formula, =COUNTA(INDEX(countsheets,0)) to get a sheet count.