399135721 has 4 divisors (see below), whose sum is σ = 416489472. Its totient is φ = 381781972.

The previous prime is 399135713. The next prime is 399135731. The reversal of 399135721 is 127531993.

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, and also an emirpimes, since its reverse is a distinct semiprime: 127531993 = 101 ⋅1262693.

It is a cyclic number.

It is not a de Polignac number, because 399135721 - 2³ = 399135713 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (399135701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8676841 + ... + 8676886.

It is an arithmetic number, because the mean of its divisors is an integer number (104122368).

Almost surely, 2^399135721 is an apocalyptic number.

It is an amenable number.

399135721 is a deficient number, since it is larger than the sum of its proper divisors (17353751).

399135721 is a wasteful number, since it uses less digits than its factorization.

399135721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17353750.

The product of its digits is 51030, while the sum is 40.

The square root of 399135721 is about 19978.3813408394. The cubic root of 399135721 is about 736.2752452182.

The spelling of 399135721 in words is "three hundred ninety-nine million, one hundred thirty-five thousand, seven hundred twenty-one".