21399839 has 2 divisors, whose sum is σ = 21399840. Its totient is φ = 21399838.

The previous prime is 21399823. The next prime is 21399901. The reversal of 21399839 is 93899312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21399839 - 2⁴ = 21399823 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21399839.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21399239) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10699919 + 10699920.

It is an arithmetic number, because the mean of its divisors is an integer number (10699920).

Almost surely, 2^21399839 is an apocalyptic number.

21399839 is a deficient number, since it is larger than the sum of its proper divisors (1).

21399839 is an equidigital number, since it uses as much as digits as its factorization.

21399839 is an evil number, because the sum of its binary digits is even.

The product of its digits is 104976, while the sum is 44.

The square root of 21399839 is about 4625.9960008629. The cubic root of 21399839 is about 277.6324136078.

The spelling of 21399839 in words is "twenty-one million, three hundred ninety-nine thousand, eight hundred thirty-nine".