21865984 has 40 divisors (see below), whose sum is σ = 49938768. Its totient is φ = 9369600.

The previous prime is 21865981. The next prime is 21865993. The reversal of 21865984 is 48956812.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21865984.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21865981) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 534 + ... + 6634.

Almost surely, 2^21865984 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 21865984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24969384).

21865984 is an abundant number, since it is smaller than the sum of its proper divisors (28072784).

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

21865984 is an frugal number, since it uses more digits than its factorization.

21865984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6126 (or 6110 counting only the distinct ones).

The product of its digits is 138240, while the sum is 43.

The square root of 21865984 is about 4676.1077831889. The cubic root of 21865984 is about 279.6338070041.

The spelling of 21865984 in words is "twenty-one million, eight hundred sixty-five thousand, nine hundred eighty-four".