169 (number)
# 169 (number)

169 (one hundred [and] sixty-nine) is the natural number following 168 and preceding 170.

## In mathematics

169 is an odd number, a composite number, and a deficient number.

169 is a square number: 13 × 13 = 169, and if each number is reversed the equation is still true: 31 × 31 = 961. 144 shares this property: 12 × 12 = 144, 21 × 21 = 441.

169 is one of the few squares to also be a centered hexagonal number. Like all odd squares, it is a centered octagonal number. 169 is an odd-indexed Pell number, thus it is also a Markov number, appearing in the solutions (2, 169, 985), (2, 29, 169), (29, 169, 14701), etc. 169 is the sum of seven consecutive primes: 13 + 17 + 19 + 23 + 29 + 31 + 37. 169 is a difference in consecutive cubes, equaling $8^{3}-7^{3}.$

## In astronomy

* 169 Zelia is a bright main belt asteroid
* Gliese 169 is an orange, main sequence (K7 V) star in the constellation Taurus
* QSO B0307+169 is a quasar in the constellation Aries
* Sayh al Uhaymir 169 is a 206g lunar meteorite found in Sultanate of Oman

## In the military

* USNS Private Jose F. Valdez (T-AG-169) was a United States Navy technical research ship during the 1960s
* USS Chatham (AK-169) was a United States Navy Alamosa-class cargo ship during World War II
* USS Gallatin (APA-169) was a United States Navy Haskell-class attack transport during World War II
* USS Foote (DD-169) was a United States Navy Wickes-class destroyer following World War I
* USS Atherton (DE-169) was a United States Navy Cannon-class destroyer escort during World War II
* USS Dolphin (SS-169) was a United States Navy submarine during World War II
* 169th Battalion, CEF unit in the Canadian Expeditionary Force during the World War I
* 169th Fires Brigade the US Army National Guard artillery brigade, a part of the Colorado Army National Guard
* The United States Air Force's 169th Fighter Wing fighter unit at McEntire Joint National Guard Station, South Carolina
* 169 or 169th Squadrons
   * 169th Airlift Squadron, a unit of the U.S. Air Force
   * Marine Light Attack Helicopter Squadron 169, United States Marine Corps Light Attack Helicopter Squadron
   * No. 169 Squadron RAF, a unit of the United Kingdom Royal Air Force

## In transportation

* Metro Transit Route 169 in Seattle
* 169th Street station on the IND Queens Boulevard Line of the New York City Subway served by the E and F trains
* 169th Street was a station on the demolished IRT Third Avenue Line of the New York City Subway

## In TV and radio

* The IEC 169-2 connector TV aerial plug

## In other fields

169 is also:

* The year AD 169 or 169 BC
* The atomic number of an element temporarily called Unhexennium
* 169 is the number of nonequivalent starting hands in the card game Texas hold 'em
* 169 is known in the computing world as the first number of an automatic IPv4 address assigned by TCP/IP when no external networking device is contactable
* Minuscule 169 is a Greek minuscule manuscript of the New Testament, on parchment
