21556871 has 4 divisors (see below), whose sum is σ = 24636432. Its totient is φ = 18477312.

The previous prime is 21556859. The next prime is 21556883. The reversal of 21556871 is 17865512.

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

It is an interprime number because it is at equal distance from previous prime (21556859) and next prime (21556883).

It is not a de Polignac number, because 21556871 - 2²² = 17362567 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 (21556841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1539770 + ... + 1539783.

It is an arithmetic number, because the mean of its divisors is an integer number (6159108).

Almost surely, 2^21556871 is an apocalyptic number.

21556871 is a deficient number, since it is larger than the sum of its proper divisors (3079561).

21556871 is an equidigital number, since it uses as much as digits as its factorization.

21556871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3079560.

The product of its digits is 16800, while the sum is 35.

The square root of 21556871 is about 4642.9377553441. The cubic root of 21556871 is about 278.3098480987.

The spelling of 21556871 in words is "twenty-one million, five hundred fifty-six thousand, eight hundred seventy-one".