21287568 has 40 divisors (see below), whose sum is σ = 55550016. Its totient is φ = 7024000.

The previous prime is 21287551. The next prime is 21287633. The reversal of 21287568 is 86578212.

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, 2653 + ... + 7043.

Almost surely, 2^21287568 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 21287568, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27775008).

21287568 is an abundant number, since it is smaller than the sum of its proper divisors (34262448).

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

21287568 is a wasteful number, since it uses less digits than its factorization.

21287568 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4503 (or 4497 counting only the distinct ones).

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

The square root of 21287568 is about 4613.8452509810. The cubic root of 21287568 is about 277.1460433160.

The spelling of 21287568 in words is "twenty-one million, two hundred eighty-seven thousand, five hundred sixty-eight".