21164821 has 4 divisors (see below), whose sum is σ = 21225132. Its totient is φ = 21104512.

The previous prime is 21164797. The next prime is 21164827. The reversal of 21164821 is 12846112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7214596 + 13950225 = 2686^2 + 3735^2 .

It is a cyclic number.

It is not a de Polignac number, because 21164821 - 2⁵ = 21164789 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 (21164827) 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, 29626 + ... + 30331.

It is an arithmetic number, because the mean of its divisors is an integer number (5306283).

Almost surely, 2^21164821 is an apocalyptic number.

It is an amenable number.

21164821 is a deficient number, since it is larger than the sum of its proper divisors (60311).

21164821 is an equidigital number, since it uses as much as digits as its factorization.

21164821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60310.

The product of its digits is 768, while the sum is 25.

The square root of 21164821 is about 4600.5239918948. The cubic root of 21164821 is about 276.6123289684.

The spelling of 21164821 in words is "twenty-one million, one hundred sixty-four thousand, eight hundred twenty-one".