669 has 4 divisors (see below), whose sum is σ = 896. Its totient is φ = 444.

The previous prime is 661. The next prime is 673. The reversal of 669 is 966.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 669 - 2³ = 661 is a prime.

It is a super-2 number, since 2×669² = 895122, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a plaindrome in base 8, base 10, base 11, base 12, base 14 and base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 109 + ... + 114.

It is an arithmetic number, because the mean of its divisors is an integer number (224).

2⁶⁶⁹ is an apocalyptic number.

It is an amenable number.

669 is a deficient number, since it is larger than the sum of its proper divisors (227).

669 is a wasteful number, since it uses less digits than its factorization.

669 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 226.

The product of its digits is 324, while the sum is 21.

The square root of 669 is about 25.8650343128. The cubic root of 669 is about 8.7459845521.

It can be divided in two parts, 6 and 69, that multiplied together give a palindrome (414).

The spelling of 669 in words is "six hundred sixty-nine", and thus it is an aban number and an oban number.