89

89 (eighty-nine) is the natural number following 88 and preceding 90.

In mathematics

Eighty-nine is the 24th prime number, following 83 and preceding 97. 89 is a Chen prime. It is the smallest Sophie Germain prime to start a Cunningham chain of the first kind of six terms, {89, 179, 359, 719, 1439, 2879}. 89 is an Eisenstein prime with no imaginary part and real part of the form 3n − 1.

89 is a Fibonacci number. Its reciprocal has a curious relationship^[1] to the Fibonacci sequence F(n):

89 is also a Markov number, appearing in solutions to the Markov Diophantine equation with other odd-indexed Fibonacci numbers.

Although 89 is not a Lychrel number in base 10, it is unusual that it takes 24 iterations of the reverse and add process to reach a palindrome. Among the known non-Lychrel numbers in the first 10000 integers, no other number requires that many or more iterations. The palindrome reached is also unusually large.^[2]

In science

• The atomic number of actinium.

In astronomy

• Messier object M89, a magnitude 11.5 elliptical galaxy in the constellation Virgo.
• The New General Catalogue object NGC 89, a magnitude 13.5 peculiar spiral galaxy in the constellation Phoenix and a member of Robert's Quartet.

In other fields

TI-89

Eighty-nine is also:

• A jersey number of a Russian and NHL hockey legend Alexander Mogilny
• The jersey number of Washington Redskins wide receiver Santana Moss
• Part of the name of the baseball team Oklahoma City 89ers (1962-1997)
• The designation of Interstate 89, a freeway that runs from New Hampshire to Vermont
• The ISBN Group Identifier for books published in Korea
• Pop Song 89
• The year AD 89, 89 BC
• California Proposition 89, a 2006 California ballot initiative on campaign finance reform
• The Oklahoma Redhawks were formerly known as the Oklahoma 89ers.
• In Rugby, a "89" or eight-nine move is a phase following a scrum, in which the number 8 catches the ball and transfers it to number 9 (scrum half).
• The greatest number of verses in a chapter of a book of the Bible other than the Book of Psalms--specifically Numbers chapter 7.
• A sexual position, much like the 69, 89 is female-> male unlike 69 which can either be male->male or female-> male, both performing oral
• The number of units of each colour in the board game Blokus
• The number of the French department Yonne

References

1. ^ Similar identities can be written for all numbers in sequence A028387 of the OEIS.
2. ^ Weisstein, Eric W. "196-Algorithm." From MathWorld, a Wolfram Web Resource. http://mathworld.wolfram.com/196-Algorithm.html