21404809 has 4 divisors (see below), whose sum is σ = 21425220. Its totient is φ = 21384400.

The previous prime is 21404741. The next prime is 21404837. The reversal of 21404809 is 90840412.

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 4717584 + 16687225 = 2172^2 + 4085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21404809 - 2⁷ = 21404681 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21404869) 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 3 ways as a sum of consecutive naturals, for example, 8542 + ... + 10759.

It is an arithmetic number, because the mean of its divisors is an integer number (5356305).

Almost surely, 2^21404809 is an apocalyptic number.

It is an amenable number.

21404809 is a deficient number, since it is larger than the sum of its proper divisors (20411).

21404809 is a wasteful number, since it uses less digits than its factorization.

21404809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20410.

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 21404809 is about 4626.5331512916. The cubic root of 21404809 is about 277.6539048332.

The spelling of 21404809 in words is "twenty-one million, four hundred four thousand, eight hundred nine".