21806839 has 4 divisors (see below), whose sum is σ = 22069656. Its totient is φ = 21544024.

The previous prime is 21806831. The next prime is 21806843. The reversal of 21806839 is 93860812.

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 21806839 - 2³ = 21806831 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a junction number, because it is equal to n+sod(n) for n = 21806798 and 21806807.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21806831) 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, 131284 + ... + 131449.

It is an arithmetic number, because the mean of its divisors is an integer number (5517414).

Almost surely, 2^21806839 is an apocalyptic number.

21806839 is a deficient number, since it is larger than the sum of its proper divisors (262817).

21806839 is an equidigital number, since it uses as much as digits as its factorization.

21806839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 262816.

The product of its (nonzero) digits is 20736, while the sum is 37.

The square root of 21806839 is about 4669.7793309749. The cubic root of 21806839 is about 279.3814534558.

The spelling of 21806839 in words is "twenty-one million, eight hundred six thousand, eight hundred thirty-nine".