21808164 has 24 divisors (see below), whose sum is σ = 58155328. Its totient is φ = 6230880.

The previous prime is 21808153. The next prime is 21808177. The reversal of 21808164 is 46180812.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 129727 + ... + 129894.

Almost surely, 2^21808164 is an apocalyptic number.

It is an amenable number.

21808164 is an abundant number, since it is smaller than the sum of its proper divisors (36347164).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21808164 is a wasteful number, since it uses less digits than its factorization.

21808164 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 259635 (or 259633 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 30.

The square root of 21808164 is about 4669.9211984786. The cubic root of 21808164 is about 279.3871118172.

Adding to 21808164 its reverse (46180812), we get a palindrome (67988976).

The spelling of 21808164 in words is "twenty-one million, eight hundred eight thousand, one hundred sixty-four".