That would be a reduplication.
"double double".
"One of the numbers is repeated twice."
There was a clue on a radio station when I was in college. The contest was to come up with the combination to a safe, 13 digits. The first caller to correctly identify the combination won the contents of the safe. One clue was broadcast each day. Our college team was on top of every clue and were the first to solve the problem. We submitted our solution after the fourth clue. The radio station had to retract one clue. "Clue #4, 'one number is repeated twice', should be 'one number is repeated'." We were not happy.
I don't like double negatives, either.
yitbos