21008821 has 8 divisors (see below), whose sum is σ = 23212224. Its totient is φ = 18912960.

The previous prime is 21008797. The next prime is 21008833. The reversal of 21008821 is 12880012.

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 21008821 - 2¹⁷ = 20877749 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21008792 and 21008801.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21008021) 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, 26475 + ... + 27256.

It is an arithmetic number, because the mean of its divisors is an integer number (2901528).

Almost surely, 2^21008821 is an apocalyptic number.

It is an amenable number.

21008821 is a deficient number, since it is larger than the sum of its proper divisors (2203403).

21008821 is a wasteful number, since it uses less digits than its factorization.

21008821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53771.

The product of its (nonzero) digits is 256, while the sum is 22.

The square root of 21008821 is about 4583.5380439132. The cubic root of 21008821 is about 275.9310415484.

Adding to 21008821 its reverse (12880012), we get a palindrome (33888833).

The spelling of 21008821 in words is "twenty-one million, eight thousand, eight hundred twenty-one".