391021 has 2 divisors, whose sum is σ = 391022. Its totient is φ = 391020.

The previous prime is 391019. The next prime is 391031. The reversal of 391021 is 120193.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 346921 + 44100 = 589^2 + 210^2 .

It is an emirp because it is prime and its reverse (120193) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 391021 - 2¹ = 391019 is a prime.

Together with 391019, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 390986 and 391004.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195510 + 195511.

It is an arithmetic number, because the mean of its divisors is an integer number (195511).

2³⁹¹⁰²¹ is an apocalyptic number.

It is an amenable number.

391021 is a deficient number, since it is larger than the sum of its proper divisors (1).

391021 is an equidigital number, since it uses as much as digits as its factorization.

391021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 54, while the sum is 16.

The square root of 391021 is about 625.3167197509. The cubic root of 391021 is about 73.1251372145.

The spelling of 391021 in words is "three hundred ninety-one thousand, twenty-one".