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