668993 has 4 divisors (see below), whose sum is σ = 720468. Its totient is φ = 617520.

The previous prime is 668989. The next prime is 668999. The reversal of 668993 is 399866.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 399866 = 2 ⋅199933.

It can be written as a sum of positive squares in 2 ways, for example, as 183184 + 485809 = 428^2 + 697^2 .

It is a cyclic number.

It is not a de Polignac number, because 668993 - 2² = 668989 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 668993.

It is not an unprimeable number, because it can be changed into a prime (668999) 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, 25718 + ... + 25743.

It is an arithmetic number, because the mean of its divisors is an integer number (180117).

2⁶⁶⁸⁹⁹³ is an apocalyptic number.

It is an amenable number.

668993 is a deficient number, since it is larger than the sum of its proper divisors (51475).

668993 is a wasteful number, since it uses less digits than its factorization.

668993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51474.

The product of its digits is 69984, while the sum is 41.

The square root of 668993 is about 817.9199227308. The cubic root of 668993 is about 87.4595404783.

It can be divided in two parts, 668 and 993, that added together give a palindrome (1661).

The spelling of 668993 in words is "six hundred sixty-eight thousand, nine hundred ninety-three".