391938021 has 20 divisors (see below), whose sum is σ = 596541132. Its totient is φ = 256359168.

The previous prime is 391937999. The next prime is 391938037. The reversal of 391938021 is 120839193.

It can be written as a sum of positive squares in 2 ways, for example, as 239909121 + 152028900 = 15489^2 + 12330^2 .

It is not a de Polignac number, because 391938021 - 2⁷ = 391937893 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (391938091) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 41356 + ... + 49941.

Almost surely, 2^391938021 is an apocalyptic number.

It is an amenable number.

391938021 is a deficient number, since it is larger than the sum of its proper divisors (204603111).

391938021 is an equidigital number, since it uses as much as digits as its factorization.

391938021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91362 (or 91353 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 36.

The square root of 391938021 is about 19797.4246052359. The cubic root of 391938021 is about 731.8225685245.

The spelling of 391938021 in words is "three hundred ninety-one million, nine hundred thirty-eight thousand, twenty-one".