Domino

The image contains 27 dominoes. A standard double-six domino set has 28 tiles representing every possible pair of numbers from 0 to 6. Upon examining the image, all possible combinations are present except for the double zero (0, 0) domino.

By systematically counting every tile in the image, I identified 27 distinct tiles. The set includes all doubles (0-0, 1-1, 2-2, 3-3, 4-4, 5-5) except for the double-six tile (6-6), which is missing from the image.

By systematically checking all 28 possible domino combinations in a standard double-six set (pairs from 0-0 through 6-6), the domino [4, 4] is the only one not present in the image. All other dominoes including [0,0], [1,1], [2,2], [3,3], [5,5], [6,6], and all mixed pairs are visible in the grid.

Scanning the 27 shown tiles I found every pair from the double-six set except the double-six tile (6-6). Therefore the excluded domino is [6,6].

After systematically identifying all 27 dominoes present in the image, the complete list includes: [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], and [6,6]. Comparing against the standard 28 dominoes in a double-six set, the only missing tile is [5,6].