80
Cardinal	eighty
Ordinal	eightieth
Numeral system	octagesimal
Factorization
Roman numeral	LXXX
Binary	01010000
Hexadecimal	50

• Greek numeral: π´
• Factors: 1, 2, 4, 5, 8, 10, 16, 20, 40, 80
• Name in other languages: quatre-vingt (in French, from four and twenty), see also wiktionary:eighty

• the atomic number of mercury (Hg)
• the number of units in a fourscore
• the age at which one becomes an octogenarian
• in the title of Around the World in Eighty Days by Jules Verne
• the model number of the computers TRS-80, IBM 80, Sinclair ZX80, Aster CT-80
• the model number of T-80, a Soviet tank; IAR 80, a Romanian WWII fighter aircraft; McDonnell Douglas MD-80, Arado Ar 80, F-80 Shooting Star
• part of the name of the bands Eighty-D and Eighty Proof Soul
• the age limit for cardinals to vote at papal conclaves
• the percentage of work done with 20% of the resources according to a "80/20 rule"
• the length of a beach in Western Australia: Eighty Mile Beach
• the length of the Eighty Years' War or Dutch revolt (1568-1648)
• the number of the French department Somme
• the designation of Interstate 80, a freeway that runs from California to New Jersey; the European route E80 from Lisbon to Gürbulak
• the standard TCP/IP port number for HTTP connection
• the year AD 80 or AD 1980.

79 and 81