689

689 is a natural number that follows 688 and precedes 690. In mathematics, it is a composite number and specifically a semiprime, since its prime factorization is 689 = 13 × 53. The divisors of 689 are 1, 13, 53, and 689.

In various representations, 689 can be written as binary 1010110001, octal 1261, and hexadecimal 0x2B1. In Roman numerals it is written as DCLXXXIX.

Several basic arithmetic properties of 689 can be noted. The sum of its digits is 6 + 8 + 9 = 23, so it is not divisible by 3 or 9, and it is not a Harshad number since 689 is not divisible by 23. It is odd and congruent to 1 modulo 8, and it is not a perfect square, triangular number, or cube.

As a semiprime with two distinct prime factors, 689 serves as a simple example in discussions of factorization and primality. In contemporary number theory and cryptography discussions, semiprimes are often used to illustrate properties that differ from primes and squares.