89

89, eighty-nine, is a natural number that follows 88 and precedes 90. It is an odd prime, and in the order of primes it sits as the 24th prime.

In mathematics, 89 is the 11th Fibonacci number (with the sequence starting 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89). As a Fibonacci prime, it is both a Fibonacci number and prime. Its base representations are 1011001 in binary and 0x59 in hexadecimal; in Roman numerals it is LXXXIX. In ASCII, the decimal code 89 corresponds to the capital letter Y. It is also a Sophie Germain prime since 2×89 + 1 = 179 is prime.

In science, the atomic number 89 belongs to actinium, the radioactive actinide element used historically in early nuclear research. Actinium occurs naturally in uranium ores and decays into thorium and other products.

In astronomy, Messier 89 (M89) is a bright elliptical galaxy in the Virgo Cluster. It is one of the many galaxies cataloged by Charles Messier and is associated with the larger structure of the Virgo constellation.

In transportation, Interstate 89 (I-89) is an Interstate Highway in the northeastern United States, running from Vermont to New Hampshire. U.S. Route 89 is a long north–south highway that traverses several western states.

Overall, 89 is notable in number theory for its primality and Fibonacci status, in science for actinium, and in astronomy for M89, reflecting the diverse contexts in which a simple two-digit number appears.