21039839 has 4 divisors (see below), whose sum is σ = 21157560. Its totient is φ = 20922120.

The previous prime is 21039817. The next prime is 21039853. The reversal of 21039839 is 93893012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21039839 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21039799 and 21039808.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21039869) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58592 + ... + 58949.

It is an arithmetic number, because the mean of its divisors is an integer number (5289390).

Almost surely, 2^21039839 is an apocalyptic number.

21039839 is a deficient number, since it is larger than the sum of its proper divisors (117721).

21039839 is a wasteful number, since it uses less digits than its factorization.

21039839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117720.

The product of its (nonzero) digits is 11664, while the sum is 35.

The square root of 21039839 is about 4586.9204266043. The cubic root of 21039839 is about 276.0667721594.

The spelling of 21039839 in words is "twenty-one million, thirty-nine thousand, eight hundred thirty-nine".