21897839 has 4 divisors (see below), whose sum is σ = 21910224. Its totient is φ = 21885456.

The previous prime is 21897809. The next prime is 21897857. The reversal of 21897839 is 93879812.

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 21897839 - 2¹⁶ = 21832303 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21897793 and 21897802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21897809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2987 + ... + 7260.

It is an arithmetic number, because the mean of its divisors is an integer number (5477556).

Almost surely, 2^21897839 is an apocalyptic number.

21897839 is a deficient number, since it is larger than the sum of its proper divisors (12385).

21897839 is a wasteful number, since it uses less digits than its factorization.

21897839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12384.

The product of its digits is 217728, while the sum is 47.

The square root of 21897839 is about 4679.5126883042. The cubic root of 21897839 is about 279.7695339966.

The spelling of 21897839 in words is "twenty-one million, eight hundred ninety-seven thousand, eight hundred thirty-nine".