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 .
89 is a Fibonacci number. The first few digits of its reciprocal coincide with the Fibonacci sequence due to the identity
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.
Read more about this topic: 89 (number)
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