[Solved] Auto index number

[catpro]

I would like to use a formula to provide an auto index number in column A based on data in column C. I will use the indexed number for lookup.

Desired Unit Name
A B C
1 1403 Christopher W Nowlin
1 1404 Christopher W Nowlin
1 1413 Christopher W Nowlin
2 1505 Thomas F Warren
2 1549 Thomas F Warren
1 1590 Christopher W Nowlin
3 1594 Dennis L English
1 1598 Christopher W Nowlin
4 1776 James Gammill
5 1817 Vincent Ricardi
5 1829 Vincent Ricardi
2 1869 Thomas F Warren
2 1872 Thomas F Warren
6 1875 Tyrel Kempson
6 1881 Tyrel Kempson
6 1882 Tyrel Kempson
Any help is greatly appreciated!

[FDibbins]

Hi catpro and welcome to the forum

what do you mean by an auto index number? what you you trying to achieve?

perhaps it would be easier to help you if you uploaded a sample workbook, showing what data you are working with, a few examples of what your expected outcome would be, and how you would arrive at that (remove any confidential info if necessary).
To attach a file to your post,
click advanced (next to quick post),
scroll down until you see "manage file",
click that and select "add files" (top right corner).
click "select files" find your file, click "open" click "upload" click 'done" bottom right. click "submit reply"

Once the upload is completed the file name will appear below the input boxes in this window.
You can then close the window to return to the new post screen.

[catpro]

Example attached.

[Teethless mama]

A5: 1
A6: =IF(COUNTIF(C$5:C5,C6),INDEX(A$5:A5,MATCH(C6,C$5:C5,0)),MAX(A$5:A5)+1)

Copy down to A20