21851904 has 72 divisors (see below), whose sum is σ = 59807440. Its totient is φ = 7077888.

The previous prime is 21851897. The next prime is 21851917. The reversal of 21851904 is 40915812.

It is a happy 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 7 ways as a sum of consecutive naturals, for example, 28032 + ... + 28800.

Almost surely, 2^21851904 is an apocalyptic number.

21851904 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21851904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29903720).

21851904 is an abundant number, since it is smaller than the sum of its proper divisors (37955536).

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

21851904 is an equidigital number, since it uses as much as digits as its factorization.

21851904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 825 (or 811 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 30.

The square root of 21851904 is about 4674.6020151452. The cubic root of 21851904 is about 279.5737732793.

The spelling of 21851904 in words is "twenty-one million, eight hundred fifty-one thousand, nine hundred four".