Twenty-five

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

• The atomic number of manganese.
• In years of marriage, silver wedding anniversary.
• The minimum age to be elected to the House of Representatives. "Under 25" is a common cut-off for designating youth.
• The number of cents in a quarter, an American coin with George Washington's portrait, and a Canadian coin.
• The designation of United States Interstate 25, a freeway that runs from New Mexico to Wyoming.
• The number of Florida electoral votes for the 2000 U.S. presidential election.

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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.