21678864 has 40 divisors (see below), whose sum is σ = 56722560. Its totient is φ = 7133568.

The previous prime is 21678823. The next prime is 21678907. The reversal of 21678864 is 46887612.

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, 934 + ... + 6650.

It is an arithmetic number, because the mean of its divisors is an integer number (1418064).

Almost surely, 2^21678864 is an apocalyptic number.

21678864 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 21678864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28361280).

21678864 is an abundant number, since it is smaller than the sum of its proper divisors (35043696).

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

21678864 is a wasteful number, since it uses less digits than its factorization.

21678864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5807 (or 5801 counting only the distinct ones).

The product of its digits is 129024, while the sum is 42.

The square root of 21678864 is about 4656.0567006857. The cubic root of 21678864 is about 278.8338574812.

The spelling of 21678864 in words is "twenty-one million, six hundred seventy-eight thousand, eight hundred sixty-four".