89 (number)

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

In mathematics

89 is:

• the 24th prime number, following 83 and preceding 97.
• a Chen prime.^[1]
• a Pythagorean prime.^[2]
• the smallest
  Sophie Germain prime to start a Cunningham chain
  of the first kind of six terms, {89, 179, 359, 719, 1439, 2879}.
• an
  Eisenstein prime
  with no imaginary part and real part of the form 3n − 1.
• a
  Fibonacci number and thus a Fibonacci prime as well.^[3]
  The first few digits of its reciprocal coincide with the Fibonacci sequence due to the identity

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

M₈₉ is the 10th Mersenne prime.

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: 8813200023188.^[4]

There are exactly 1000 prime numbers between 1 and 89²=7921. ^[5]

In science

Eighty-nine is:

• The atomic number of actinium.

In astronomy

• magnitude 11.5 elliptical galaxy in the constellation Virgo.^[6]
• 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 sports

• The
  white settlement. The team's home of Oklahoma City
  was founded during this event.
• In
  Rugby
  , an "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
  grade point average
  .
• Liverpool and Arsenal in 1989
  .

Eighty-nine is also:

• The designation of Interstate 89, a freeway that runs from New Hampshire to Vermont^[7]
• The designation of U.S. Route 89, a north–south highway that runs from Montana to Arizona
• The ISBN Group Identifier for books published in Korea
• "Pop Song 89" by R.E.M.
• A model of the Texas Instruments calculator TI-89
• California
  Proposition 89
  , a 2006 California ballot initiative on campaign finance reform
• The title of a currently-unreleased song by Bon Iver
• The greatest number of verses in a chapter of a book of the Bible other than the Book of Psalms—specifically Numbers chapter 7.
• The number of units of each colour in the board game Blokus
• The number of the French department Yonne
• eighty-nine as one of the words censored on the Chinese internet.^[8]