The 91 (number) reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

91 (number)

91 is the natural number following 90 and preceding 92.

List of numbers — Integers << 90 91 92 93 94 95 96 97 98 99 >>
Cardinal	ninety-one
Ordinal	91st (ninety-first)
Factorization
Roman numeral	LXXVIII
Binary	1001110
Hexadecimal	4E

In mathematics

Ninety-one is a triangular number and a hexagonal number, one of the few such numbers to also be a centered hexagonal number. It is the sum of the squares of the first six integers.

It is also the smallest pseudoprime satisfying the congruence .

In other fields

Ninety-one is also:

• The atomic number of protactinium, an actinide.
• The designation of American Interstate 91, a freeway that runs from Connecticut to Vermont.
• The code for international direct dial phone calls to India.
• In cents of a U.S. dollar, the amount of money one has if one has one each of the coins of denominations less than a dollar (penny, nickel, dime, quarter and half dollar).
• The year AD 91, 91 BC, or 1991.

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