21855839 has 2 divisors, whose sum is σ = 21855840. Its totient is φ = 21855838.

The previous prime is 21855817. The next prime is 21855877. The reversal of 21855839 is 93855812.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21855839 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21855796 and 21855805.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21855139) 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 as a sum of consecutive naturals, namely, 10927919 + 10927920.

It is an arithmetic number, because the mean of its divisors is an integer number (10927920).

Almost surely, 2^21855839 is an apocalyptic number.

21855839 is a deficient number, since it is larger than the sum of its proper divisors (1).

21855839 is an equidigital number, since it uses as much as digits as its factorization.

21855839 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 86400, while the sum is 41.

The square root of 21855839 is about 4675.0228876445. The cubic root of 21855839 is about 279.5905537662.

The spelling of 21855839 in words is "twenty-one million, eight hundred fifty-five thousand, eight hundred thirty-nine".