21865872 has 80 divisors (see below), whose sum is σ = 65710080. Its totient is φ = 6135936.

The previous prime is 21865843. The next prime is 21865891. The reversal of 21865872 is 27856812.

It is a self number, because there is not a number n which added to its sum of digits gives 21865872.

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 15 ways as a sum of consecutive naturals, for example, 19273 + ... + 20375.

It is an arithmetic number, because the mean of its divisors is an integer number (821376).

Almost surely, 2^21865872 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 21865872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32855040).

21865872 is an abundant number, since it is smaller than the sum of its proper divisors (43844208).

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

21865872 is a wasteful number, since it uses less digits than its factorization.

21865872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1180 (or 1174 counting only the distinct ones).

The product of its digits is 53760, while the sum is 39.

The square root of 21865872 is about 4676.0958074017. The cubic root of 21865872 is about 279.6333295648.

The spelling of 21865872 in words is "twenty-one million, eight hundred sixty-five thousand, eight hundred seventy-two".