668021 has 4 divisors (see below), whose sum is σ = 703200. Its totient is φ = 632844.

The previous prime is 668009. The next prime is 668029. The reversal of 668021 is 120866.

668021 = 79² + 80² + ... + 135².

668021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-668021 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668029) 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, 17561 + ... + 17598.

It is an arithmetic number, because the mean of its divisors is an integer number (175800).

2⁶⁶⁸⁰²¹ is an apocalyptic number.

It is an amenable number.

668021 is a deficient number, since it is larger than the sum of its proper divisors (35179).

668021 is a wasteful number, since it uses less digits than its factorization.

668021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35178.

The product of its (nonzero) digits is 576, while the sum is 23.

The square root of 668021 is about 817.3255165477. The cubic root of 668021 is about 87.4171624175.

Adding to 668021 its reverse (120866), we get a palindrome (788887).

The spelling of 668021 in words is "six hundred sixty-eight thousand, twenty-one".