21687568 has 40 divisors (see below), whose sum is σ = 48621888. Its totient is φ = 9178752.

The previous prime is 21687559. The next prime is 21687581. The reversal of 21687568 is 86578612.

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 7 ways as a sum of consecutive naturals, for example, 8130 + ... + 10462.

Almost surely, 2^21687568 is an apocalyptic number.

21687568 is a gapful number since it is divisible by the number (28) 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 21687568, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24310944).

21687568 is an abundant number, since it is smaller than the sum of its proper divisors (26934320).

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

21687568 is a wasteful number, since it uses less digits than its factorization.

21687568 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2431 (or 2425 counting only the distinct ones).

The product of its digits is 161280, while the sum is 43.

The square root of 21687568 is about 4656.9913034061. The cubic root of 21687568 is about 278.8711694788.

The spelling of 21687568 in words is "twenty-one million, six hundred eighty-seven thousand, five hundred sixty-eight".