21002809 has 8 divisors (see below), whose sum is σ = 22211840. Its totient is φ = 19804176.

The previous prime is 21002797. The next prime is 21002857. The reversal of 21002809 is 90820012.

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 21002809 - 2⁵ = 21002777 is a prime.

It is a super-2 number, since 2×21002809² = 882235971780962, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21002809.

It is not an unprimeable number, because it can be changed into a prime (21002899) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1759 + ... + 6715.

It is an arithmetic number, because the mean of its divisors is an integer number (2776480).

Almost surely, 2^21002809 is an apocalyptic number.

It is an amenable number.

21002809 is a deficient number, since it is larger than the sum of its proper divisors (1209031).

21002809 is a wasteful number, since it uses less digits than its factorization.

21002809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5199.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21002809 is about 4582.8821717343. The cubic root of 21002809 is about 275.9047183881.

The spelling of 21002809 in words is "twenty-one million, two thousand, eight hundred nine".