21181808 has 20 divisors (see below), whose sum is σ = 43200360. Its totient is φ = 10033344.

The previous prime is 21181807. The next prime is 21181837. The reversal of 21181808 is 80818112.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21181801) 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, 34535 + ... + 35142.

It is an arithmetic number, because the mean of its divisors is an integer number (2160018).

Almost surely, 2^21181808 is an apocalyptic number.

It is an amenable number.

21181808 is an abundant number, since it is smaller than the sum of its proper divisors (22018552).

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

21181808 is a wasteful number, since it uses less digits than its factorization.

21181808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69704 (or 69698 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 29.

The square root of 21181808 is about 4602.3698243405. The cubic root of 21181808 is about 276.6863126966.

The spelling of 21181808 in words is "twenty-one million, one hundred eighty-one thousand, eight hundred eight".