i'd say either 3,6 or 8, you would have to try and identify any die markers to be sure, which could be tough or impossible due to wear..
I'm leaning more towards a very worn 8. http://coppercoins.com/lincoln/diestate.php?date=1972&die_id=1972p1do008&die_state=eds
Hard for me to tell from 8 or 6. I would be more inclined to 6 but I can't see the die markers, Obv or the chips and die scratches rev.