391331021 has 4 divisors (see below), whose sum is σ = 391602912. Its totient is φ = 391059132.

The previous prime is 391330969. The next prime is 391331033. The reversal of 391331021 is 120133193.

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 391331021 - 2⁶ = 391330957 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 (391331051) 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, 133775 + ... + 136668.

It is an arithmetic number, because the mean of its divisors is an integer number (97900728).

Almost surely, 2^391331021 is an apocalyptic number.

It is an amenable number.

391331021 is a deficient number, since it is larger than the sum of its proper divisors (271891).

391331021 is a wasteful number, since it uses less digits than its factorization.

391331021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 271890.

The product of its (nonzero) digits is 486, while the sum is 23.

The square root of 391331021 is about 19782.0883882365. The cubic root of 391331021 is about 731.4445786433. Note that the first 3 decimals are identical.

The spelling of 391331021 in words is "three hundred ninety-one million, three hundred thirty-one thousand, twenty-one".