Domino

A standard double-six set contains 28 tiles. After inspecting the 27 tiles in the image, all tiles except the [0, 6] (blank and six) are present. The list of pairs identified includes [2, 5], [0, 4], [4, 6], [3, 6], [2, 6], [1, 2], [2, 4], [4, 4], [3, 3], [2, 3], [1, 4], [0, 3], [5, 5], [0, 0], [5, 6], [1, 3], [0, 5], [6, 6], [0, 2], [3, 5], [3, 4], [4, 5], [1, 1], [1, 5], [2, 2], [0, 1], and [1, 6].

The excluded domino is number 2 and 1

After systematically examining all 27 dominoes visible in the image and cross-referencing against the complete standard double-six set of 28 tiles, the domino [4, 4] is missing. All other dominoes representing combinations of numbers 0-6, including [0,0], [1,1], [2,2], [3,3], [5,5], [6,6] and all mixed pairs, are present in the image. The double-four ([4,4]) is the only tile from the complete set that is absent.

By systematically cataloging all visible dominoes in the image and comparing against a complete standard double-six domino set (28 tiles), the tile showing 0-3 (blank/three) is not present among the 27 displayed dominoes.

I examined each tile and tallied the unordered pairs shown; every combination from 0–6 appears except the domino containing 5 and 6, so the missing tile is [5,6].

The image contains 27 dominoes. A standard double-six set contains 28 dominoes. By identifying all the double tiles (tiles with identical numbers on both ends), I can see [0,0], [1,1], [2,2], [3,3], [4,4], and [5,5] are all present in the image. The only double tile missing from this sequence is [6,6]. Additionally, while several dominoes containing 6 are visible ([2,6], [3,6], [5,6]), the [6,6] tile is not present, confirming it is the excluded domino.