668821 has 2 divisors, whose sum is σ = 668822. Its totient is φ = 668820.

The previous prime is 668813. The next prime is 668851. The reversal of 668821 is 128866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 476100 + 192721 = 690^2 + 439^2 .

It is a cyclic number.

It is not a de Polignac number, because 668821 - 2³ = 668813 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (668851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334410 + 334411.

It is an arithmetic number, because the mean of its divisors is an integer number (334411).

2⁶⁶⁸⁸²¹ is an apocalyptic number.

It is an amenable number.

668821 is a deficient number, since it is larger than the sum of its proper divisors (1).

668821 is an equidigital number, since it uses as much as digits as its factorization.

668821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 31.

The square root of 668821 is about 817.8147712043. The cubic root of 668821 is about 87.4520444704.

The spelling of 668821 in words is "six hundred sixty-eight thousand, eight hundred twenty-one".