80

80 is the natural number that follows 79 and precedes 81. In decimal notation it is written as 80. It is an even, composite number with prime factorization 2^4 × 5, and it has 10 positive divisors: 1, 2, 4, 5, 8, 10, 16, 20, 40, and 80. The sum of its proper divisors is 106, so 80 is an abundant number with abundance 26.

In various numeral systems, 80 has representations such as binary 1010000, octal 120, and hexadecimal 0x50. In Roman numerals it is LXXX. Its Unicode/ASCII value 80 corresponds to the uppercase letter P. In mathematics 80 can be expressed as 8^2 + 4^2, and Euler's totient φ(80) = 32.

Attention to 80 in applied contexts: in computing networks, port 80 is the standard port for unencrypted HTTP traffic. The element mercury has atomic number 80 (symbol Hg), a dense liquid metal at room temperature. The decimal 80 also equates to about 26.7 degrees Celsius or about 80 degrees Fahrenheit in temperature conversions; 80°F equals 26.7°C approximately.

Historically, year 80 AD saw the completion of the Colosseum in Rome under Emperor Titus. The number is used in culture and measurement as a round figure in ages, anniversaries, and scoring; but numerically it is primarily noted for its factorization and representations.