Eighty-nine is prime and reduces to seventeen and then eight. Its interest is mathematical: it is a term in the Fibonacci sequence, the eleventh, following fifty-five and preceding a hundred and forty-four, and it is prime as well, one of the relatively few Fibonacci primes, which recreational mathematics notes with pleasure. The reciprocal of eighty-nine, moreover, generates the Fibonacci numbers in its decimal expansion, a curiosity that has been much enjoyed. Beyond these arithmetical properties the number carries no traditional symbolism.
In chemistry, eighty-nine is the atomic number of actinium, from the Greek aktis, aktinos, ray or beam, discovered in 1899 by Andre-Louis Debierne.
Eighty-nine is prime, with no factors beyond one and itself. Because it leaves a remainder of one when divided by four, it is a Pythagorean prime, expressible as a sum of two squares: 5 squared plus 8 squared. It further qualifies as a Sophie Germain prime, since doubling it and adding one also yields a prime, properties recreational number theory tracks but that carry no symbolic weight of their own.
The whole apparatus of digit-reduction numerology is a twentieth-century invention rather than an inheritance from antiquity. Mrs. L. Dow Balliett published the first systematic version, The Philosophy of Numbers, in 1908, fixing the letter-to-number chart still used today and ruling that eleven and twenty-two must stand as master numbers rather than reduce further; her colleague, the physician Julia Seton, is credited with coining the word numerology itself around 1912.