Domino

By systematically checking all 28 possible domino combinations (0-0 through 6-6), I identified all dominoes present in the image. The domino [2, 4] (or equivalently [4, 2]) is the only combination that does not appear anywhere in the 27 tiles shown.

After listing and counting all tiles in the image, the 27 tiles present are [1,5], [0,3], [0,1], [4,5], [0,0], [5,6], [2,6], [5,5], [4,6], [2,2], [3,3], [1,1], [0,6], [0,4], [3,4], [1,2], [4,4], [1,6], [6,6], [3,5], [2,4], [2,3], [1,4], [3,6], [0,5], [0,2], and [1,3]. Comparing this to a standard 28-tile double-six set, the [6, 4] domino is the only one missing.

I systematically catalogued all visible dominoes in the image. A standard double-six set has 28 tiles. After identifying all 27 visible dominoes and checking which combination from 0-0 through 6-6 is missing, the domino [0,3] (blank-three) is not present in the image.

After carefully examining the ASCII art representation of the 27 dominoes and comparing against the complete double-six set of 28 unique tiles (0-0 through 6-6), the tile representing 5 and 3 is absent. All other combinations are present.

The excluded domino is number 2 and 2

By analyzing the visible dominoes and counting the occurrences of each number, I found that the number 4 appears exactly 7 times across the visible tiles, while all other numbers appear 8 times. The visible dominoes containing 4 are: [0|4], [1|4], [2|4], [3|4], [4|4], and [4|6]. Since each number should appear 8 times in a complete set (appearing on 7 dominoes plus the double), and the number 4 appears only 7 times, the missing domino must be the one that would contribute the 8th occurrence of 4, which is [4|5]. Similarly, counting 5s: [0|5], [1|5], [2|5], [3|5], [5|5], and [5|6] are present (7 occurrences), confirming that [4|5] is the excluded domino.