21108021 has 8 divisors (see below), whose sum is σ = 30702624. Its totient is φ = 12792720.

The previous prime is 21108007. The next prime is 21108047. The reversal of 21108021 is 12080112.

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

It is not a de Polignac number, because 21108021 - 2⁹ = 21107509 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21108821) 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, 319786 + ... + 319851.

It is an arithmetic number, because the mean of its divisors is an integer number (3837828).

Almost surely, 2^21108021 is an apocalyptic number.

It is an amenable number.

21108021 is a deficient number, since it is larger than the sum of its proper divisors (9594603).

21108021 is a wasteful number, since it uses less digits than its factorization.

21108021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 639651.

The product of its (nonzero) digits is 32, while the sum is 15.

The square root of 21108021 is about 4594.3466347240. The cubic root of 21108021 is about 276.3646592412.

Adding to 21108021 its reverse (12080112), we get a palindrome (33188133).

The spelling of 21108021 in words is "twenty-one million, one hundred eight thousand, twenty-one".