399159721 has 4 divisors (see below), whose sum is σ = 405925200. Its totient is φ = 392394244.

The previous prime is 399159713. The next prime is 399159727. The reversal of 399159721 is 127951993.

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 not a de Polignac number, because 399159721 - 2³ = 399159713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (399159727) 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, 3382651 + ... + 3382768.

It is an arithmetic number, because the mean of its divisors is an integer number (101481300).

Almost surely, 2^399159721 is an apocalyptic number.

It is an amenable number.

399159721 is a deficient number, since it is larger than the sum of its proper divisors (6765479).

399159721 is an equidigital number, since it uses as much as digits as its factorization.

399159721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6765478.

The product of its digits is 153090, while the sum is 46.

The square root of 399159721 is about 19978.9819810720. The cubic root of 399159721 is about 736.2900023136.

The spelling of 399159721 in words is "three hundred ninety-nine million, one hundred fifty-nine thousand, seven hundred twenty-one".