How to insert Auto serial number in merged cells

how to auto fill serial number in merged cells,
put serial number in merged excel cells,
how to add serial number in merged cells,
how to automatically add serial number in ms excel,
how to automatically insert serial number in ms excel,
serial number formula in merged cells in excel,
serial number in merged cells,
auto numbering in merged cells,
excelshortsvideo,
how we can insert serial numbers in merged cells,
excel video tutorial,
excel tricks,
office experts