21851808 has 48 divisors (see below), whose sum is σ = 62578656. Its totient is φ = 6621440.

The previous prime is 21851789. The next prime is 21851813. The reversal of 21851808 is 80815812.

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (33).

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, 9291 + ... + 11402.

It is an arithmetic number, because the mean of its divisors is an integer number (1303722).

Almost surely, 2^21851808 is an apocalyptic number.

It is an amenable number.

21851808 is an abundant number, since it is smaller than the sum of its proper divisors (40726848).

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

21851808 is a wasteful number, since it uses less digits than its factorization.

21851808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20717 (or 20709 counting only the distinct ones).

The product of its (nonzero) digits is 5120, while the sum is 33.

The square root of 21851808 is about 4674.5917468801. The cubic root of 21851808 is about 279.5733638699.

It can be divided in two parts, 2185 and 1808, that added together give a palindrome (3993).

The spelling of 21851808 in words is "twenty-one million, eight hundred fifty-one thousand, eight hundred eight".