• 26 is the seventh discrete semiprime (${\displaystyle 2\times 13}$ ) ^[1] and the fifth with 2 as the lowest non-unitary factor thus of the form (2.q), where q is a higher prime.
• 26 is the smallest even number n such that both n + 1 and n − 1 are composite.
• With an aliquot sum of 16, within an aliquot sequence of five composite numbers (26,16,15,9,4,3,1,0) to the Prime in the 3-aliquot tree.
• 26 is the only integer that is one greater than a square (5² + 1) and one less than a cube (3³ − 1).^[2]
• 26 is a telephone number, specifically, the number of ways of connecting 5 points with pairwise connections.^[3]
• There are 26 sporadic groups.^[4]
• The 26-dimensional Lorentzian unimodular lattice II_25,1 plays a significant role in sphere packing problems and the classification of finite simple groups. In particular, the Leech lattice is obtained in a simple way as a subquotient.
• 26 is the smallest number that is both a nontotient and a noncototient number.
• 26 is the number of permutations of {a, b, c, d, e} with only one ascent.^[5][a]
• There are 26 faces of a rhombicuboctahedron.^[6]
• When a 3 × 3 × 3 cube is made of 27 unit cubes (e.g. Rubik's Cube), 26 of them are viewable as the exterior layer.
• A cube has 26 elements: 6 faces, 12 edges, and 8 vertices.
• A 26-sided polygon is called an icosihexagon.^[7]
• φ(26) = φ(σ(26)).^[8]

Twenty-six is a repdigit in base three (222₃) and in base 12 (22₁₂).

In base ten, 26 is the smallest positive integer that is not a palindrome to have a square (26² = 676) that is a palindrome.

• 26 is the gematric number, being the sum of the Hebrew characters (Hebrew: יהוה) being the name of the god of Israel – YHWH (Yahweh).
• 26 is also the gematric number for GOD with the corresponding substitutions in English (i.e. A=1, B=2, C=3, and so on)

• Prime Curios! 26 from the Prime Pages