21709568 has 36 divisors (see below), whose sum is σ = 43721160. Its totient is φ = 10758144.

The previous prime is 21709553. The next prime is 21709573. The reversal of 21709568 is 86590712.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 34763 + ... + 35381.

Almost surely, 2^21709568 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 21709568, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21860580).

21709568 is an abundant number, since it is smaller than the sum of its proper divisors (22011592).

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

21709568 is an equidigital number, since it uses as much as digits as its factorization.

21709568 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 772 (or 758 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 38.

The square root of 21709568 is about 4659.3527447490. The cubic root of 21709568 is about 278.9654338116.

The spelling of 21709568 in words is "twenty-one million, seven hundred nine thousand, five hundred sixty-eight".