659

This number is a prime.

The first occurrence of a twin prime pair (659, 661) one of which is strobogrammatic and the other one invertible when read on a calculator (7-segment digital display). Note that the latter when turned upside down becomes also the larger member of another twin prime pair (197, 199). [Beedassy]

0659, 2659, 3659, 5659, and 6659 are all primes. [Forouhati]

There is a binary star system in the constellation Cygnus consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years.

The number of correct decimal digits produced by the fifth iteration of the cubic Borwein-Borwein algorithm for computing 1/π. [Ekhad]