Auto Sequential Invoice number on a duplicate sheet

[learnerspermit]

I've created an Invoice Template in excel. I create new invoices by creating duplicate sheet and infilling new customer information in the relevant cells. Each time I create a duplicate sheet, I'd like a certain cell "F4" to increase by one number starting at 200. Please give me the very basics on how to do this. I am an excel dummy so please help. I have attached a template for illustration purposes.

[vlady]

Are you trying to "create a copy" of the template then renaming the template say "Sheet2" is that correct??

the formula below will rely on the Sheetname Number

=100&LOOKUP(99^99,--("0"&MID(CELL("filename"),MIN(SEARCH({0,1,2,3,4,5,6,7,8,9},CELL("filename")&"0123456789")),ROW($1:$10000))))