Domino

After counting all 27 dominoes in the image and cross-referencing them with a standard 28-tile double-six set, the [5, 6] tile is the only one not present.

By systematically checking all 28 possible dominoes in a standard double-six set, I identified that the domino [2, 5] is missing from the 27 tiles shown in the image. All other combinations of numbers from 0-6 are present.

I systematically identified all 28 dominoes in a standard double-six set and compared them to the 27 shown in the image. After cataloging each visible domino, the tile [0,3] (blank-three) was the one not present in the image.

The excluded domino is number 3 and 3

I counted the pips on all 54 visible halves. Every digit 0–6 appears seven times except for 3 and 6, which each appear only six times, so the missing tile pairs a 3 with a 6 (the [3,6] domino).

By analyzing the visible dominoes in the image and counting the occurrences of each number, the double-one domino [1,1] is the only one from the standard double-six set that cannot be found. All other dominoes including [0,0], [2,2], [3,3], [4,4], and [6,6] are present or can be accounted for, while [1,1] (which would show a single dot on both halves) is missing from the arrangement.