Domino

The image contains 27 dominoes. A standard double-six domino set has 28 tiles. Upon inspection, all possible pairs from 0 to 6 are represented except for the double-three domino.

A standard double-six domino set contains 28 tiles. By cataloging all tiles in the image, we find that 27 are present: [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 [5,6]. The only tile missing from the set is the [6,6] double-six tile.

I systematically checked all 28 possible dominoes in a standard double-six set. By examining each domino visible in the image and cross-referencing against the complete set of all combinations from [0,0] through [6,6], the domino [1,4] is the only one not present in the image. All other 27 unique combinations are visible among the displayed tiles.

Every other tile from the double-six set is present in the image; the only domino not shown is the double six [6,6].

By systematically cataloging all visible dominoes in the image and comparing them to the complete set of 28 dominoes (0-0 through 6-6), I identified that the domino with values 0 and 3 is missing from the set.

By counting the occurrences of each number on the halves, numbers 0,1,2,4,6 appear 8 times each, while 3 and 5 appear 7 times each, indicating the missing domino is [3-5].

By analyzing the 27 dominoes present in the image, all dominoes involving combinations of numbers 0-3 are accounted for, as well as several higher combinations. However, the domino connecting 0 and 4 (the [0-4] tile) is not present among the visible tiles, while [0-0], [0-1], [0-2], [0-3] are present and [1-4] is present, indicating the 0-series and 4-series are nearly complete except for the [0-4] combination.