21856891 has 12 divisors (see below), whose sum is σ = 26247360. Its totient is φ = 18128880.

The previous prime is 21856889. The next prime is 21856903. The reversal of 21856891 is 19865812.

It is not a de Polignac number, because 21856891 - 2¹ = 21856889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21856801) 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 11 ways as a sum of consecutive naturals, for example, 5676 + ... + 8713.

It is an arithmetic number, because the mean of its divisors is an integer number (2187280).

Almost surely, 2^21856891 is an apocalyptic number.

21856891 is a deficient number, since it is larger than the sum of its proper divisors (4390469).

21856891 is a wasteful number, since it uses less digits than its factorization.

21856891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14434 (or 14427 counting only the distinct ones).

The product of its digits is 34560, while the sum is 40.

The square root of 21856891 is about 4675.1353991088. The cubic root of 21856891 is about 279.5950395933.

The spelling of 21856891 in words is "twenty-one million, eight hundred fifty-six thousand, eight hundred ninety-one".