55

55 is the natural number following 54 and preceding 56. In mathematics, 55 is a composite number with prime factorization 5 × 11, making it a semiprime. Its positive divisors are 1, 5, 11, and 55. It is the tenth triangular number, since 10 × 11 / 2 equals 55. In different numeral systems, 55 is represented as LV in Roman numerals, 110111 in binary, and 0x37 in hexadecimal. In ASCII, the decimal code 55 corresponds to the character '7'.

55 is the atomic number of cesium, a soft alkali metal used in various applications, including atomic clocks and ion propulsion research.

Cultural and infrastructural uses: The number is associated with highways designated with the number 55, such as Interstate 55. The phrase “I Can’t Drive 55” refers to a 1984 song by Van Halen, and the United States maintained a nationwide 55 mph speed limit from the 1970s to 1995 under the Emergency Highway Energy Conservation Act.

55 Cancri is a star in the constellation Cancer; it hosts multiple exoplanets, including 55 Cancri e, a well-known close-in planet.