581 = 7 x 83.
581 is the sum of three consecutive primes: 191 + 193 + 197 = 581.
581 has a base 3 representation (210112) that begins with its base 4 representation (21011).
581 becomes a prime when 3 is prefixed or appended: 3581 and 5813 are primes.
Gliese 581 c was the first discovered terrestrial exosolar planet in the habitable zone surrounding its star (where the surface temperatures might be similar to Earth's).
Source: Wikipedia
