165 (one hundred [and] sixty-five) is the natural number following 164 and preceding 166.

In mathematics

165 is:

• an odd number, a composite number, and a deficient number.
• a sphenic number.
• a tetrahedral number^[1]
• the sum of the sums of the divisors of the first 14 positive integers.^[2]
• a self number in base 10.
• a palindromic number in binary (10100101₂) and bases 14 (BB₁₄), 32 (55₃₂) and 54 (33₅₄).
• a unique period in base 2.

In astronomy

• 165 Loreley is a large Main belt asteroid
• 165P/LINEAR is a periodic comet in the Solar System
• The planet Neptune takes about 165 years to orbit the Sun.

In the military

• Caproni Ca.165 Italian fighter aircraft developed before World War II
• USNS American Explorer (T-AOT-165) was a United States Navy tanker, part of the U.S. Reserve Fleet, Beaumont, Texas
• USS Bonita (SS-165) was a United States Navy Barracuda-class submarine during World War II
• USS Bullock (AK-165) was a United States Navy Alamosa-class cargo ship during World War II
• USS Counsel (AM-165) was a United States Navy Admirable-class minesweeper during World War II
• USS Counsel (AM-165) was a United States Navy Haskell-class attack transport during World War II
• USS Flicker (IX-165) was a United States Navy minesweeper during World War II
• USS Georgetown (AG-165) was a United States Navy Oxford-class technical research ship following World War II
• USS Meredith (DD-165) was a United States Navy Wickes-class destroyer during World War I
• USS Parks (DE-165) was a United States Navy Cannon-class destroyer escort during World War II
• USS Prince Georges (AP-165) was a United States Navy Crater-class transport and cargo ship during World War II
• USS Wenonah (SP-165) was a United States Navy yacht during World War I
• The 165 Squadron, Republic of Singapore Air Force Air Defence Operations Command, Republic of Singapore Air Force

In transportation

• British Rail Class 165
• The Blériot 165 was a French four-engine biplane airliner of the early 1920s
• The Cessna 165 single-engine plane of the 1930s
• LOT Polish Airlines Flight 165, en route from Warsaw to Cracow Balice airport crashed during a snowstorm on April 2, 1969

In other fields

165 is also:

• The year AD 165 or 165 BC
• 165 AH is a year in the Islamic calendar that corresponds to 781 – 782 CE
• The atomic number of an element temporarily called Unhexpentium
• G.165 is a Telecommunication Standardization Sector standard for echo cancellers, used in telephony
• The human gene Zinc finger protein 165, or ZNF165