Multiple Copy and Paste with Adding

I've made a spreadsheet that needs the product ID number to increase by 1 every time a new sheet is produced.

I can get it to look at the previous sheet and add 1 using ='SHEET1'!A1+1 but I have alter the sheet number every time a new sheet is added (I add approx 20 at a time).

Can I alter the formula so it will automatically look at the previous sheet then add 1?

are you apposed to macros to do this?