399821 has 4 divisors (see below), whose sum is σ = 405372. Its totient is φ = 394272.

The previous prime is 399793. The next prime is 399851. The reversal of 399821 is 128993.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 346921 + 52900 = 589^2 + 230^2 .

It is a cyclic number.

It is not a de Polignac number, because 399821 - 2⁶ = 399757 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 (399851) 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, 2666 + ... + 2811.

It is an arithmetic number, because the mean of its divisors is an integer number (101343).

2³⁹⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

399821 is a deficient number, since it is larger than the sum of its proper divisors (5551).

399821 is an equidigital number, since it uses as much as digits as its factorization.

399821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5550.

The product of its digits is 3888, while the sum is 32.

The square root of 399821 is about 632.3140042732. The cubic root of 399821 is about 73.6696376390.

The spelling of 399821 in words is "three hundred ninety-nine thousand, eight hundred twenty-one".