21105857 has 16 divisors (see below), whose sum is σ = 23188032. Its totient is φ = 19130880.

The previous prime is 21105811. The next prime is 21105863. The reversal of 21105857 is 75850112.

It is a cyclic number.

It is not a de Polignac number, because 21105857 - 2¹⁴ = 21089473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21105457) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 74438 + ... + 74720.

It is an arithmetic number, because the mean of its divisors is an integer number (1449252).

Almost surely, 2^21105857 is an apocalyptic number.

It is an amenable number.

21105857 is a deficient number, since it is larger than the sum of its proper divisors (2082175).

21105857 is a wasteful number, since it uses less digits than its factorization.

21105857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 448.

The product of its (nonzero) digits is 2800, while the sum is 29.

The square root of 21105857 is about 4594.1111218602. Note that the first 4 decimals coincide. The cubic root of 21105857 is about 276.3552145920.

Adding to 21105857 its reverse (75850112), we get a palindrome (96955969).

The spelling of 21105857 in words is "twenty-one million, one hundred five thousand, eight hundred fifty-seven".