Home > 81 (number)
Integers Composite numbers81 is the natural number following 80 and preceding 82.
Eighty-one is a square and a heptagonal number.
It is also a tribonacci number, an open meandric number and a Harshad numberA Harshad number or Niven number is an integer that is divisible by the sum of its digits in a given number base. The Niven numbers take their name from Ivan M. Niven from a paper delivered at a conference on number theory in 1997. All numbers between zer.
Eighty-one is also:
- the atomic numberThe atomic number Z is a term used in chemistry and physics to represent the number of protons found in the nucleus of an atom. In an atom of neutral charge, the number of electrons typically equals the atomic number. The atomic number originally meant th of thalliummercury thallium lead In Tl Uut Full table General Name, Symbol, NumberThallium, Tl, 81 Chemical series Poor metals Group, Period, Block 13 (IIIA), 6 , p Density, Hardness 11850 kg/m³, 1. 2 Appearance Silvery white Atomic properties Atomic weight 204. (Tl)
- the title of a short film by Stephen Burke: 81
- the model number of: Unterseeboot 81Unterseeboot 81 (U-81 has been the designation of two submarines of the German Navy. During World War I, U-81 was launched on 24 June 1916, and commissioned into the Kaiserliche Marine on August 22, 1916. The second U-81 was a Type VIIC submarine of the K, Sinclair ZX81The Sinclair ZX81 home computer, released by Sinclair Research in 1981, was the followup to the company's ZX80. The case was black, with a membrane keyboard; the machine's distinctive appearance was the work of industrial designer Rick Dickinson. Video ou
- the Messier number of the M81 Group of galaxies
- the number of the French department Tarn
- the designation of Interstate 81, a freeway that runs from Tennessee to New York.
- the code for international direct dial phone calls to Japan
- the number of times a popular rhyme (erroneously) claims Lizzie Borden struck her parents with an axe
- One of two ISBN Group Identifiers for books published in India
- The year AD 81, 81 BC, or 1981.
