857540821 has 4 divisors (see below), whose sum is σ = 857605644. Its totient is φ = 857476000.

The previous prime is 857540807. The next prime is 857540837. The reversal of 857540821 is 128045758.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 641862225 + 215678596 = 25335^2 + 14686^2 .

It is a 3-Lehmer number, since φ(857540821) divides (857540821-1)³.

It is a cyclic number.

It is not a de Polignac number, because 857540821 - 2⁹ = 857540309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (857540861) 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, 4630 + ... + 41671.

It is an arithmetic number, because the mean of its divisors is an integer number (214401411).

Almost surely, 2^857540821 is an apocalyptic number.

857540821 is the 18521-st heptagonal number.

It is an amenable number.

857540821 is a deficient number, since it is larger than the sum of its proper divisors (64823).

857540821 is a wasteful number, since it uses less digits than its factorization.

857540821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64822.

The product of its (nonzero) digits is 89600, while the sum is 40.

The square root of 857540821 is about 29283.7979264985. The cubic root of 857540821 is about 950.0612411121.

The spelling of 857540821 in words is "eight hundred fifty-seven million, five hundred forty thousand, eight hundred twenty-one".