81 may refer to: *

81 (number) 81 (eighty-one) is the natural number following 80 (number), 80and preceding 82 (number), 82. In mathematics 81 is: * the square number, square of 9 (number), 9 and the second fourth-power of a prime; 34. * with an aliquot sum of 40 (number), 40; ...

* one of the years 81 BC, AD 81, 1981,

2081 In contemporary history, the third millennium is the current millennium in the ''Anno Domini'' or Common Era, under the Gregorian calendar. It began on 1 January 2001 (Roman numerals, MMI) and will end on 31 December 3000 (Roman numerals, MMM ...

* The international calling code for

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

* Nickname for the Hells Angels Motorcycle Club. "H" is the eighth letter of the alphabet, and "A" is the first. * 81 Terpsichore, a main-belt asteroid * 81 mm mortar, a military indirect fire weapon

See also