129 (one hundred [and] twenty-nine) is the natural number following 128 and preceding 130.

In mathematics

129 is the sum of the first ten prime numbers. It is the smallest number that can be expressed as a sum of three squares in four different ways: ${\displaystyle 11^{2}+2^{2}+2^{2))$, ${\displaystyle 10^{2}+5^{2}+2^{2))$, ${\displaystyle 8^{2}+8^{2}+1^{2))$, and ${\displaystyle 8^{2}+7^{2}+4^{2))$.

129 is the product of only two primes, 3 and 43, making 129 a semiprime. Since 3 and 43 are both Gaussian primes, this means that 129 is a Blum integer.^[1]

129 is a repdigit in base 6 (333).

129 is a happy number.^[2]

129 is a centered octahedral number.^[3]

In the military

• Raytheon AGM-129 ACM (Advanced Cruise Missile) was a low observable, sub-sonic, jet-powered, air-launched cruise missile used by the United States Air Force
• Soviet submarine K-129 (1960) was a Soviet Pacific Fleet nuclear submarine that sank in 1968
• USNS Mission San Miguel (T-AO-129) was a United States Navy Mission Buenaventura-class fleet oilers during World War II
• USS Donald W. Wolf (APD-129) was a Crosley-class high speed transport of the United States Navy
• USS Edsall (DE-129) was the lead ship of her class of destroyer escort in the United States Navy
• USS Marvin H. McIntyre (APA-129) was a United States Navy Haskell-class attack transport during World War II
• USS Phobos (AK-129) was a United States Navy Crater-class cargo ship during World War II
• USS Vital (AM-129) was a United States Navy Auk-class minesweeper for removing naval mines laid in the water
• Agusta A129 Mangusta is an attack helicopter originally designed and produced by Italian company Agusta
• The 129th Rescue Wing (129 RQW) is a unit of the California Air National Guard

In transportation

• LZ 129 Hindenburg was a German zeppelin which went up in flames while landing on May 6, 1937
• London Buses route 129 is a Transport for London contracted bus route in London
• STS-129 was a Space Shuttle mission to the International Space Station, flown in November 2009 by the shuttle Atlantis.

In other fields

129 is also:

• The year AD 129 or 129 BC
• 129 AH is a year in the Islamic calendar that corresponds to 746–747 CE
• 129 Antigone is a main belt asteroid
• The atomic number of unbiennium, an element yet to be discovered
• A film format: 129 film
• Sonnet 129 by William Shakespeare