181 (number)

In mathematics

• 181 is an odd number
• 181 is a centered number
• * 181 is a centered pentagonal number
• * 181 is a centered 12-gonal number
• * 181 is a centered 18-gonal number
• * 181 is a centered 30-gonal number
• * 181 is a centered square number
• * 181 is a star number that represents a centered hexagram
• 181 is a deficient number, as 1 is less than 181
• 181 is an odious number
• 181 is a prime number
• * 181 is a Chen prime
• * 181 is a dihedral prime
• * 181 is a full reptend prime
• * 181 is a palindromic prime
• * 181 is a strobogrammatic prime, the same when viewed upside down
• * 181 is a twin prime with 179
• 181 is a square-free number
• 181 is an undulating number, if written in the ternary, the negaternary, or the nonary numeral systems
• 181 is the difference of 2 square numbers: 91² – 90²
• 181 is the sum of 2 consecutive square numbers: 9² + 10²
• 181 is the sum of 5 consecutive prime numbers: 29 + 31 + 37 + 41 + 43

  In geography

• Langenburg No. 181, Saskatchewan rural municipality in Saskatchewan, Canada
• 181 Fremont Street proposed skyscraper in San Francisco, California
• 181 West Madison Street, Chicago

  In the military

• 181st Battalion, CEF was a unit in the Canadian Expeditionary Force during World War I
• 181st Airlift Squadron is a unit of the Texas Air National Guard
• 181st Infantry Brigade of the United States Army based at Fort McCoy, Wisconsin
• 181st Intelligence Wing is a unit of the United States Air Force located at Hulman Field, Terre Haute, Indiana
• AN/APQ-181 an all-weather, low probability of intercept radar system for the U.S. Air Force B-2A Spirit bomber aircraft
• Bücker Bü 181 Bestmann single-engine trainer aircraft during World War II
• was a ship scheduled to be acquired by the United States Navy, however, the program was cancelled
• was a United States Navy troop transport during World War II
• was a United States Navy oiler following the Vietnam War
• was a United States Navy ATA-174-class auxiliary ocean tugboat during World War II
• was a United States Navy Alamosa-class cargo ship following World War II
• was a United States Navy following World War I
• was a United States Navy Porpoise-class submarine during World War II
• was a United States Navy during World War II

  In movies

• “,” winner of the 2005 Yamagata International Documentary Film Festival
• The war film “The Enemy Below” revolves around the fictitious, USS Hayes and a German U-boat

  In transportation

• The Volkswagen 181
• Lufthansa Flight 181, which was hijacked on October 13, 1977
• London Buses route 181
• 181 Union City-New York, a New Jersey Transit bus route from New Jersey to New York
• The Córas Iompair Éireann CIE 181 Class diesel locomotives, and numbered B181 to B192, built by General Motors Electro-Motive Division in 1966
• East 181st Avenue, a light rail station on the MAX Blue Line in Gresham, Oregon
• New York City Subway stations in Manhattan:
• * 181st Street, at Fort Washington Avenue served by the
• * 181st Street, at St. Nicholas Avenue served by the
• 181st Street
• Oregon Route 229, also known as the Siletz Highway No. 181

  In other fields

• The year AD 181 or 181 BC
• The atomic number of an element temporarily called
• 181 Eucharis is a large K-type Main belt asteroid
• Minuscule 181, α 101, is a Greek minuscule manuscript of the New Testament
• Mir-181 microRNA precursor is a small non-coding RNA molecule
• The number of channels on an older American television set, with 68 over-the-air television channels and 113 cable television channels