399165921 has 32 divisors (see below), whose sum is σ = 737280000. Its totient is φ = 207357840.

The previous prime is 399165917. The next prime is 399165929. The reversal of 399165921 is 129561993.

It is a happy number.

It is not a de Polignac number, because 399165921 - 2² = 399165917 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (399165929) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 93921 + ... + 98078.

It is an arithmetic number, because the mean of its divisors is an integer number (23040000).

Almost surely, 2^399165921 is an apocalyptic number.

It is an amenable number.

399165921 is a deficient number, since it is larger than the sum of its proper divisors (338114079).

399165921 is a wasteful number, since it uses less digits than its factorization.

399165921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 192026 (or 192020 counting only the distinct ones).

The product of its digits is 131220, while the sum is 45.

The square root of 399165921 is about 19979.1371435305. The cubic root of 399165921 is about 736.2938144671.

The spelling of 399165921 in words is "three hundred ninety-nine million, one hundred sixty-five thousand, nine hundred twenty-one".