Domino

By systematically checking all 28 possible domino combinations (0-0 through 6-6, where each pair is counted once), I can account for 27 dominoes visible in the image. The domino [4, 4] (double-four) is the only combination from the standard set that is not present among the displayed tiles.

By systematically checking the 28 tiles of a standard double-six set against the 27 tiles in the image, all tiles except for [4, 6] are found. The present tiles are: [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], [5,5], [5,6], [6,6]. The [4, 6] tile is missing.

The domino [0, 0] is missing from the given image of 27 dominoes.

By systematically going through all 28 dominoes in a standard double-six set and comparing with the image, I can identify which one is missing. The standard set includes all combinations from (0,0) to (6,6). After carefully examining each domino in the image, the (0,3) domino appears to be the one not present in the image.

Counting the pips on each half of the 27 visible tiles shows the counts for 1 and 4 are each one less than expected for a complete double-six set, so the missing domino is [1,4].

After identifying all 27 dominoes in the image, I found that all doubles are present except [5,5]. The doubles [0,0], [1,1], [2,2], [3,3], [4,4], and [6,6] are all visible in the set, leaving [5,5] as the only missing tile from the standard double-six set of 28 dominoes.