Domino

The image contains 27 dominoes. A standard double-six domino set has 28 tiles. Upon examining the image, it is evident that the domino [6, 6] is missing, as there is no tile with 6 dots on both halves.

After cataloging all 27 dominoes in the image, the missing tile from the standard double-six set (28 tiles) is [0, 6], also known as the blank-six tile.

By systematically checking all 28 possible dominoes in a standard double-six set (all pairs of numbers 0-6 inclusive), the domino [4,4] is the only one not visible in the image. All other dominoes from [0,0] through [6,6] can be identified among the 27 tiles shown.

By systematically cataloging all visible dominoes in the image and comparing them against the complete set of 28 dominoes (0-0 through 6-6), I identified that the domino with values 0 and 4 is missing from the set.

After carefully examining the image and counting the pips on each half of the 27 dominoes shown, I listed all unique pairs (normalized with lower number first). Comparing to the complete double-six set of 28 dominoes (all pairs [i,j] with 0 ≤ i ≤ j ≤ 6), the missing one is [2,5].

I counted the visible tiles and identified every tile from the standard double-six set except the double six; the [6,6] tile does not appear among the 27 shown.

By systematically identifying all visible dominoes in the image and counting the occurrences of each number, I determined that the double-six domino [6,6] is the only one missing from the standard set. I identified the presence of [0,0], [1,1], [2,2], [3,3], and [4,4] among the doubles, and found multiple dominoes with 6 on one side ([2,6], [3,6]) but no domino with 6 on both sides. The missing domino must be [6,6].