21597857 has 4 divisors (see below), whose sum is σ = 22124676. Its totient is φ = 21071040.

The previous prime is 21597833. The next prime is 21597859. The reversal of 21597857 is 75879512.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11669056 + 9928801 = 3416^2 + 3151^2 .

It is a cyclic number.

It is not a de Polignac number, because 21597857 - 2¹⁰ = 21596833 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21597859) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 263348 + ... + 263429.

It is an arithmetic number, because the mean of its divisors is an integer number (5531169).

Almost surely, 2^21597857 is an apocalyptic number.

It is an amenable number.

21597857 is a deficient number, since it is larger than the sum of its proper divisors (526819).

21597857 is an equidigital number, since it uses as much as digits as its factorization.

21597857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 526818.

The product of its digits is 176400, while the sum is 44.

The square root of 21597857 is about 4647.3494596383. The cubic root of 21597857 is about 278.4861195965.

The spelling of 21597857 in words is "twenty-one million, five hundred ninety-seven thousand, eight hundred fifty-seven".