399721 has 8 divisors (see below), whose sum is σ = 483840. Its totient is φ = 322368.

The previous prime is 399719. The next prime is 399727. The reversal of 399721 is 127993.

399721 is nontrivially palindromic in base 6.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 399721 - 2¹ = 399719 is a prime.

399721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (399727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1561 + ... + 1798.

It is an arithmetic number, because the mean of its divisors is an integer number (60480).

2³⁹⁹⁷²¹ is an apocalyptic number.

It is an amenable number.

399721 is a deficient number, since it is larger than the sum of its proper divisors (84119).

399721 is a wasteful number, since it uses less digits than its factorization.

399721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3383.

The product of its digits is 3402, while the sum is 31.

The square root of 399721 is about 632.2349246918. The cubic root of 399721 is about 73.6634952419.

The spelling of 399721 in words is "three hundred ninety-nine thousand, seven hundred twenty-one".