821391 has 4 divisors (see below), whose sum is σ = 1095192. Its totient is φ = 547592.

The previous prime is 821383. The next prime is 821411. The reversal of 821391 is 193128.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 821391 - 2³ = 821383 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821311) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136896 + ... + 136901.

It is an arithmetic number, because the mean of its divisors is an integer number (273798).

2⁸²¹³⁹¹ is an apocalyptic number.

821391 is a deficient number, since it is larger than the sum of its proper divisors (273801).

821391 is a wasteful number, since it uses less digits than its factorization.

821391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 273800.

The product of its digits is 432, while the sum is 24.

The square root of 821391 is about 906.3062396343. The cubic root of 821391 is about 93.6519116305.

The spelling of 821391 in words is "eight hundred twenty-one thousand, three hundred ninety-one".