21362809 has 4 divisors (see below), whose sum is σ = 23006116. Its totient is φ = 19719504.

The previous prime is 21362753. The next prime is 21362827. The reversal of 21362809 is 90826312.

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 1755625 + 19607184 = 1325^2 + 4428^2 .

It is a cyclic number.

It is not a de Polignac number, because 21362809 - 2¹¹ = 21360761 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21362839) 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, 821634 + ... + 821659.

It is an arithmetic number, because the mean of its divisors is an integer number (5751529).

Almost surely, 2^21362809 is an apocalyptic number.

It is an amenable number.

21362809 is a deficient number, since it is larger than the sum of its proper divisors (1643307).

21362809 is a wasteful number, since it uses less digits than its factorization.

21362809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1643306.

The product of its (nonzero) digits is 5184, while the sum is 31.

The square root of 21362809 is about 4621.9918866220. The cubic root of 21362809 is about 277.4721839933.

The spelling of 21362809 in words is "twenty-one million, three hundred sixty-two thousand, eight hundred nine".