i want to enter a row is a serial number column and wanted if any row is inserted all the numbers are still in a serial number for example.

1
2
3
4
5
6
7

this is a original sequence column.now what i want to do is

1
2
3

4
5
6
7
a row is inserted and i want to enter a number in the cell so that all the numbers in the column are still in sequence

Please reply it is urgent

Thanks & Regards,
Deeppak