21801808 has 20 divisors (see below), whose sum is σ = 48275680. Its totient is φ = 9343584.

The previous prime is 21801743. The next prime is 21801811. The reversal of 21801808 is 80810812.

It is a Harshad number since it is a multiple of its sum of digits (28).

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 3 ways as a sum of consecutive naturals, for example, 97218 + ... + 97441.

It is an arithmetic number, because the mean of its divisors is an integer number (2413784).

Almost surely, 2^21801808 is an apocalyptic number.

21801808 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21801808 is an abundant number, since it is smaller than the sum of its proper divisors (26473872).

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

21801808 is a wasteful number, since it uses less digits than its factorization.

21801808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 194674 (or 194668 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 28.

The square root of 21801808 is about 4669.2406234847. The cubic root of 21801808 is about 279.3599666767.

The spelling of 21801808 in words is "twenty-one million, eight hundred one thousand, eight hundred eight".