21989839 has 2 divisors, whose sum is σ = 21989840. Its totient is φ = 21989838.

The previous prime is 21989837. The next prime is 21989861. The reversal of 21989839 is 93898912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21989839 - 2¹ = 21989837 is a prime.

Together with 21989837, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21989792 and 21989801.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21989833) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10994919 + 10994920.

It is an arithmetic number, because the mean of its divisors is an integer number (10994920).

Almost surely, 2^21989839 is an apocalyptic number.

21989839 is a deficient number, since it is larger than the sum of its proper divisors (1).

21989839 is an equidigital number, since it uses as much as digits as its factorization.

21989839 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 279936, while the sum is 49.

The square root of 21989839 is about 4689.3324684863. The cubic root of 21989839 is about 280.1607877533.

The spelling of 21989839 in words is "twenty-one million, nine hundred eighty-nine thousand, eight hundred thirty-nine".