21537821 has 8 divisors (see below), whose sum is σ = 22576320. Its totient is φ = 20507872.

The previous prime is 21537787. The next prime is 21537851. The reversal of 21537821 is 12873512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21537821 - 2¹⁰ = 21536797 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 (21537851) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3350 + ... + 7368.

It is an arithmetic number, because the mean of its divisors is an integer number (2822040).

Almost surely, 2^21537821 is an apocalyptic number.

It is an amenable number.

21537821 is a deficient number, since it is larger than the sum of its proper divisors (1038499).

21537821 is a wasteful number, since it uses less digits than its factorization.

21537821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4275.

The product of its digits is 3360, while the sum is 29.

The square root of 21537821 is about 4640.8857990690. The cubic root of 21537821 is about 278.2278423023.

The spelling of 21537821 in words is "twenty-one million, five hundred thirty-seven thousand, eight hundred twenty-one".