21001856 has 32 divisors (see below), whose sum is σ = 42742080. Its totient is φ = 10274560.

The previous prime is 21001847. The next prime is 21001861. The reversal of 21001856 is 65810012.

It is a tau number, because it is divible by the number of its divisors (32).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4271 + ... + 7761.

It is an arithmetic number, because the mean of its divisors is an integer number (1335690).

Almost surely, 2^21001856 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21371040).

21001856 is an abundant number, since it is smaller than the sum of its proper divisors (21740224).

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

21001856 is an equidigital number, since it uses as much as digits as its factorization.

21001856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3552 (or 3540 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 23.

The square root of 21001856 is about 4582.7781966838. The cubic root of 21001856 is about 275.9005452769.

Adding to 21001856 its reverse (65810012), we get a palindrome (86811868).

The spelling of 21001856 in words is "twenty-one million, one thousand, eight hundred fifty-six".