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Twenty-five (25, XXV) is the natural number following twenty-four and preceding twenty-six. It is a square number, being 52 = 5 × 5, and it is also the sum of two squares, 32 + 42. It is also a Cullen number. 25 is the smallest pseudoprime satisfying the congruence 7n = 7 mod n. It is also a Somer pseudoprime based on 6.

In base 10, it is easy to test for divisibility by 25, by seeing if the last two digits of the number are 25, 50, 75 or 00.

Twenty-five is also

See also: twenty-three, twenty-four, twenty-six, twenty-seven, integer, list of numbers.

This article is about the number. For the year AD 25, see 25.