21500857 has 6 divisors (see below), whose sum is σ = 25011258. Its totient is φ = 18429264.

The previous prime is 21500833. The next prime is 21500893. The reversal of 21500857 is 75800512.

It can be written as a sum of positive squares in only one way, i.e., 20830096 + 670761 = 4564^2 + 819^2 .

It is not a de Polignac number, because 21500857 - 2¹⁹ = 20976569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21500827) 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 5 ways as a sum of consecutive naturals, for example, 219348 + ... + 219445.

It is an arithmetic number, because the mean of its divisors is an integer number (4168543).

Almost surely, 2^21500857 is an apocalyptic number.

It is an amenable number.

21500857 is a deficient number, since it is larger than the sum of its proper divisors (3510401).

21500857 is an equidigital number, since it uses as much as digits as its factorization.

21500857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438807 (or 438800 counting only the distinct ones).

The product of its (nonzero) digits is 2800, while the sum is 28.

The square root of 21500857 is about 4636.9016595136. The cubic root of 21500857 is about 278.0685828756.

The spelling of 21500857 in words is "twenty-one million, five hundred thousand, eight hundred fifty-seven".