21808005 has 16 divisors (see below), whose sum is σ = 35385984. Its totient is φ = 11466560.

The previous prime is 21807959. The next prime is 21808013. The reversal of 21808005 is 50080812.

It is not a de Polignac number, because 21808005 - 2¹⁷ = 21676933 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 9174 + ... + 11303.

It is an arithmetic number, because the mean of its divisors is an integer number (2211624).

Almost surely, 2^21808005 is an apocalyptic number.

It is an amenable number.

21808005 is a deficient number, since it is larger than the sum of its proper divisors (13577979).

21808005 is a wasteful number, since it uses less digits than its factorization.

21808005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20556.

The product of its (nonzero) digits is 640, while the sum is 24.

The square root of 21808005 is about 4669.9041746057. The cubic root of 21808005 is about 279.3864328259.

Adding to 21808005 its reverse (50080812), we get a palindrome (71888817).

The spelling of 21808005 in words is "twenty-one million, eight hundred eight thousand, five".