80 (number)

In mathematics

• the sum of Euler's totient function φ over the first sixteen integers.
• a semiperfect number, since adding up some subsets of its divisors gives 80.
• a ménage number.
• palindromic in bases 3, 6, 9, 15, 19 and 39.
• a repdigit in bases 3, 9, 15, 19 and 39.

In science

• The atomic number of mercury

  In religion

• According to Exodus 7:7, Moses was 80 years old when he initially spoke to Pharaoh on behalf of his people. Today, 80 years of age is the upper age limit for cardinals to vote in papal elections.

  In other fields

• used in the classic book title Around the World in Eighty Days
• the length of the Eighty Years' War or Dutch revolt
• the standard TCP/IP port number for HTTP connections
• the 80A, 80B and 80C photographic filters correct for excessive redness under tungsten lighting
• The year AD 80, 80 BC, or 1980
• Eighty shilling ale
• The older four-pin-base version of the 5Y3GT rectifier tube
• A common limit for the characters per line, in computing, derived from the number of columns in IBM cards
• American band Green Day has a song called "80"
• A fictional alien superhero named Ultraman 80