Auto Numbering in a column

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.

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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

thanks it solved the problem