21621839 has 4 divisors (see below), whose sum is σ = 21639024. Its totient is φ = 21604656.

The previous prime is 21621823. The next prime is 21621851. The reversal of 21621839 is 93812612.

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 21621839 - 2⁴ = 21621823 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621139) 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, 6542 + ... + 9275.

It is an arithmetic number, because the mean of its divisors is an integer number (5409756).

Almost surely, 2^21621839 is an apocalyptic number.

21621839 is a deficient number, since it is larger than the sum of its proper divisors (17185).

21621839 is a wasteful number, since it uses less digits than its factorization.

21621839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17184.

The product of its digits is 5184, while the sum is 32.

The square root of 21621839 is about 4649.9289241880. The cubic root of 21621839 is about 278.5891573451.

The spelling of 21621839 in words is "twenty-one million, six hundred twenty-one thousand, eight hundred thirty-nine".