25 (number)

25 is the sum of the five consecutive single-digit odd natural numbers 1, 3, 5, 7, and 9.

It is the smallest decimal Friedman number as it can be expressed by its own digits: 52.

[7] 25 is the smallest pseudoprime satisfying the congruence 7n = 7 mod n. 25 is the smallest aspiring number — a composite non-sociable number whose aliquot sequence does not terminate.

Within decimal, one can readily test for divisibility by 25 by seeing if the last two digits of the number match 00, 25, 50, or 75.

symmetry in the fourth dimension can be arranged in two distinct manners, such that The 24-cell can be further generated using three copies of the 8-cell, where the 24-cell honeycomb is dual to the 16-cell honeycomb (with the tesseract the dual polytope to the 16-cell).

, to the cannonball problem where sum of the squares of the first twenty-five natural numbers

[12] The Leech lattice, meanwhile, is constructed in multiple ways, one of which is through copies of the

lattice in eight dimensions[13] isomorphic to the 600-cell,[14] where twenty-five 24-cells fit; a set of these twenty-five integers can also generate the twenty-fourth triangular number, whose value twice over is