Because 4t means 4 multiplied by t, using it as variable conflicts with expression which 4t. For example, 8n conflicts with n(we write 8n to mean 8 times n), so it conflicts with a mathematical expression. Excel doesn't allow variables like GN23423 if it conflicts with an existing cell name. It means there are 1,048,576 rows in Excel and 16,384 columns in Excel. If it only contains an alphabetical string and a number(starts with a string of one or more letters and one or more numbers after the letters), make sure that the number is greater than 1,048,576, and letter is after XFD. Variables like snow329 are valid but not it104 because Excel isn't case sensitive in variable names.