21428839 has 4 divisors (see below), whose sum is σ = 21450280. Its totient is φ = 21407400.

The previous prime is 21428831. The next prime is 21428861. The reversal of 21428839 is 93882412.

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

It is a cyclic number.

It is not a de Polignac number, because 21428839 - 2³ = 21428831 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21428798 and 21428807.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21428831) 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, 9144 + ... + 11245.

It is an arithmetic number, because the mean of its divisors is an integer number (5362570).

Almost surely, 2^21428839 is an apocalyptic number.

21428839 is a deficient number, since it is larger than the sum of its proper divisors (21441).

21428839 is a wasteful number, since it uses less digits than its factorization.

21428839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21440.

The product of its digits is 27648, while the sum is 37.

The square root of 21428839 is about 4629.1293997900. The cubic root of 21428839 is about 277.7577682238.

The spelling of 21428839 in words is "twenty-one million, four hundred twenty-eight thousand, eight hundred thirty-nine".