The 81 (number) reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

81 (number)

81 is the natural number following 80 and preceding 82.

List of numbers — Integers << 80 81 82 83 84 85 86 87 88 89 >>
Cardinal	eighty-one
Ordinal	81st (eighty-first)
Factorization
Divisors	3, 9, 27
Roman numeral	LXXXI
Binary	01010001
Hexadecimal	51

Eighty-one is a square and a heptagonal number. It is also a tribonacci number and a meandric number.

Eighty-one is also:

• the atomic number of thallium (Tl)
• the title of a short film by Stephen Burke: 81
• the model number of: Unterseeboot 81, Sinclair ZX81
• 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 year AD 81, 81 BC, or 1981.

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