21855439 has 2 divisors, whose sum is σ = 21855440. Its totient is φ = 21855438.

The previous prime is 21855437. The next prime is 21855487. The reversal of 21855439 is 93455812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21855439 - 2¹ = 21855437 is a prime.

Together with 21855437, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21855398 and 21855407.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21855437) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10927719 + 10927720.

It is an arithmetic number, because the mean of its divisors is an integer number (10927720).

Almost surely, 2^21855439 is an apocalyptic number.

21855439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21855439 is an equidigital number, since it uses as much as digits as its factorization.

21855439 is an evil number, because the sum of its binary digits is even.

The product of its digits is 43200, while the sum is 37.

The square root of 21855439 is about 4674.9801069095. The cubic root of 21855439 is about 279.5888480908.

The spelling of 21855439 in words is "twenty-one million, eight hundred fifty-five thousand, four hundred thirty-nine".