857821 has 2 divisors, whose sum is σ = 857822. Its totient is φ = 857820.

The previous prime is 857809. The next prime is 857827. The reversal of 857821 is 128758.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 688900 + 168921 = 830^2 + 411^2 .

It is a cyclic number.

It is not a de Polignac number, because 857821 - 2⁹ = 857309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (857827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 428910 + 428911.

It is an arithmetic number, because the mean of its divisors is an integer number (428911).

2⁸⁵⁷⁸²¹ is an apocalyptic number.

It is an amenable number.

857821 is a deficient number, since it is larger than the sum of its proper divisors (1).

857821 is an equidigital number, since it uses as much as digits as its factorization.

857821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4480, while the sum is 31.

The square root of 857821 is about 926.1862663633. The cubic root of 857821 is about 95.0164699053.

The spelling of 857821 in words is "eight hundred fifty-seven thousand, eight hundred twenty-one".