21856171 has 4 divisors (see below), whose sum is σ = 22023144. Its totient is φ = 21689200.

The previous prime is 21856151. The next prime is 21856189. The reversal of 21856171 is 17165812.

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

It is a cyclic number.

It is not a de Polignac number, because 21856171 - 2⁵ = 21856139 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21856151) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 83290 + ... + 83551.

It is an arithmetic number, because the mean of its divisors is an integer number (5505786).

Almost surely, 2^21856171 is an apocalyptic number.

21856171 is a deficient number, since it is larger than the sum of its proper divisors (166973).

21856171 is a wasteful number, since it uses less digits than its factorization.

21856171 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166972.

The product of its digits is 3360, while the sum is 31.

The square root of 21856171 is about 4675.0583953572. The cubic root of 21856171 is about 279.5919694611.

The spelling of 21856171 in words is "twenty-one million, eight hundred fifty-six thousand, one hundred seventy-one".