155 (number)

155 (one hundred [and] fifty-five) is the natural number following 154 and preceding 156.

In mathematics
155 is:
 * a composite number
 * a semiprime.
 * a deficient number, since 1+5+31=37<155.
 * odious, since its binary expansion $$10011011_2$$ has a total of 5 ones in it.

There are 155 primitive permutation groups of degree 81.

If one adds up all the primes from the least through the greatest prime factors of 155, that is, 5 and 31, the result is 155. Only three other "small" semiprimes (10, 39, and 371) share this attribute.

In the military

 * USS Capable (AM-155) was a United States Navy Admirable-class minesweeper during World War II
 * USS Cole (DD-155) was a United States Navy Wickes-class destroyer during World War II
 * USS General A. W. Brewster (AP-155) was a United States Navy General G. O. Squier-class transport during World War II
 * USS Hopping (DE-155) was a United States Navy Buckley-class destroyer escort during World War II
 * USS Lycoming (APA-155) was a United States Navy Haskell-class attack transport during World War II
 * USS Mustang (IX-155) was a United States Navy four-master wooden schooner during World War II
 * 155mm artillery, a common caliber

In sports

 * The maximum possible score in a single break in snooker, with a free ball at the start of the break (147 is the highest possible without a free ball)

In transportation

 * Alfa Romeo 155, a compact executive car produced from 1992 to 1998
 * Seattle Bus Route 155
 * London Bus Route 155
 * The British Rail Class 155 is a diesel multiple unit British train
 * Blériot 155 was a French airliner of the 1920s
 * 155th Street, Manhattan, New York
 * 155th Street New York City Subway stations:
 * 155th Street (IND Concourse Line)
 * 155th Street (IND Eighth Avenue Line)
 * 155th Street (IRT Ninth Avenue Line) (former)

In other fields
155 is also:
 * The year AD 155 or 155 BC
 * 155 is the number for the International Operator in the United Kingdom
 * 155 is the number for the emergency medical services in the Czech Republic and Slovakia
 * 155 AH is a year in the Islamic calendar that corresponds to 771–772 CE
 * 155 Scylla is a main belt asteroid
 * Europium-155 is a radioisotope or Europium and fission product with a half-life of 4.76 years
 * 155, a 2007 song by the band +44
 * The dialing code for Obihiro, Japan
 * The atomic number of an element temporarily called unquintquinttium
 * 155 North Wacker is a 46-story skyscraper in Chicago
 * Wolseley No. 155, Saskatchewan, is a rural municipality in Canada