668649 has 4 divisors (see below), whose sum is σ = 891536. Its totient is φ = 445764.

The previous prime is 668623. The next prime is 668671. The reversal of 668649 is 946866.

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 668649 - 2⁵ = 668617 is a prime.

It is a D-number.

It is a Duffinian number.

It is a Curzon number.

668649 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (668609) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111439 + ... + 111444.

It is an arithmetic number, because the mean of its divisors is an integer number (222884).

2⁶⁶⁸⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

668649 is a deficient number, since it is larger than the sum of its proper divisors (222887).

668649 is a wasteful number, since it uses less digits than its factorization.

668649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 222886.

The product of its digits is 62208, while the sum is 39.

The square root of 668649 is about 817.7096061561. The cubic root of 668649 is about 87.4445471773. Note that the first 3 decimals are identical.

The spelling of 668649 in words is "six hundred sixty-eight thousand, six hundred forty-nine".