391238721 has 8 divisors (see below), whose sum is σ = 579612960. Its totient is φ = 260825796.

The previous prime is 391238699. The next prime is 391238737. The reversal of 391238721 is 127832193.

It is not a de Polignac number, because 391238721 - 2⁷ = 391238593 is a prime.

It is not an unprimeable number, because it can be changed into a prime (391238791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7245135 + ... + 7245188.

It is an arithmetic number, because the mean of its divisors is an integer number (72451620).

Almost surely, 2^391238721 is an apocalyptic number.

It is an amenable number.

391238721 is a deficient number, since it is larger than the sum of its proper divisors (188374239).

391238721 is a wasteful number, since it uses less digits than its factorization.

391238721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14490332 (or 14490326 counting only the distinct ones).

The product of its digits is 18144, while the sum is 36.

The square root of 391238721 is about 19779.7553321572. The cubic root of 391238721 is about 731.3870675342.

The spelling of 391238721 in words is "three hundred ninety-one million, two hundred thirty-eight thousand, seven hundred twenty-one".