391787921 has 8 divisors (see below), whose sum is σ = 458170944. Its totient is φ = 328008240.

The previous prime is 391787897. The next prime is 391787953. The reversal of 391787921 is 129787193.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 391787921 - 2²⁶ = 324679057 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (391787521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 650510 + ... + 651111.

It is an arithmetic number, because the mean of its divisors is an integer number (57271368).

Almost surely, 2^391787921 is an apocalyptic number.

It is an amenable number.

391787921 is a deficient number, since it is larger than the sum of its proper divisors (66383023).

391787921 is a wasteful number, since it uses less digits than its factorization.

391787921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1301671.

The product of its digits is 190512, while the sum is 47.

The square root of 391787921 is about 19793.6333450936. The cubic root of 391787921 is about 731.7291348801.

The spelling of 391787921 in words is "three hundred ninety-one million, seven hundred eighty-seven thousand, nine hundred twenty-one".