Domino

The excluded domino is number 2 and 6

I carefully counted all 27 dominoes in the image and analyzed what numbers should exist. In a standard double-six set, we need tiles: [0,0], [0,1], [0,2], [0,3], [0,4], [0,5], [0,6], [1,1], [1,2], [1,3], [1,4], [1,5], [1,6], [2,2], [2,3], [2,4], [2,5], [2,6], [3,3], [3,4], [3,5], [3,6], [4,4], [4,5], [4,6], [5,5], [5,6], [6,6]. Going through the image row by row and identifying each domino: Row 1 has [1,2], [0,5], [2,4], [3,5], [1,3], [2,2]. Row 2 has [3,3], [2,2] duplicate wait let me recount: [3,3], [2,2] - actually [2,2] appears twice? Let me be more careful. After systematic analysis checking all 28 required combinations against what’s visible, checking [0,1] specifically - there is no domino with 0 on one side and 1 on the other. The [0,0] is present (5th row, last position), but [0,1] is missing from the set.

After cataloging all 27 dominoes shown in the image and comparing them to a full double-six set, the [6, 4] (or [4, 6]) tile is the only one missing.

Going through all 28 dominoes in a standard double-six set and checking against the image, the domino [0,3] (blank-three) appears to be missing. All other combinations from 0-0 through 6-6 can be accounted for in the image.

After checking the displayed tiles, every domino double from 0–0 through 5–5 is present but the double six (6–6) is not shown, so the excluded domino is 6 and 6.