391238921 has 8 divisors (see below), whose sum is σ = 395131464. Its totient is φ = 387365760.

The previous prime is 391238917. The next prime is 391238963. The reversal of 391238921 is 129832193.

It can be written as a sum of positive squares in 4 ways, for example, as 1729225 + 389509696 = 1315^2 + 19736^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 391238921 - 2² = 391238917 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (391238821) 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, 37535 + ... + 46811.

It is an arithmetic number, because the mean of its divisors is an integer number (49391433).

Almost surely, 2^391238921 is an apocalyptic number.

It is an amenable number.

391238921 is a deficient number, since it is larger than the sum of its proper divisors (3892543).

391238921 is a wasteful number, since it uses less digits than its factorization.

391238921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9691.

The product of its digits is 23328, while the sum is 38.

The square root of 391238921 is about 19779.7603878308. The cubic root of 391238921 is about 731.3871921618.

The spelling of 391238921 in words is "three hundred ninety-one million, two hundred thirty-eight thousand, nine hundred twenty-one".