21687264 has 72 divisors (see below), whose sum is σ = 63980280. Its totient is φ = 7226496.

The previous prime is 21687251. The next prime is 21687287. The reversal of 21687264 is 46278612.

It is a tau number, because it is divible by the number of its divisors (72).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6382 + ... + 9170.

It is an arithmetic number, because the mean of its divisors is an integer number (888615).

Almost surely, 2^21687264 is an apocalyptic number.

21687264 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 21687264, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31990140).

21687264 is an abundant number, since it is smaller than the sum of its proper divisors (42293016).

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

21687264 is an equidigital number, since it uses as much as digits as its factorization.

21687264 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2814 (or 2794 counting only the distinct ones).

The product of its digits is 32256, while the sum is 36.

The square root of 21687264 is about 4656.9586641928. The cubic root of 21687264 is about 278.8698664707.

The spelling of 21687264 in words is "twenty-one million, six hundred eighty-seven thousand, two hundred sixty-four".