21521568 has 96 divisors (see below), whose sum is σ = 59524416. Its totient is φ = 6801408.

The previous prime is 21521557. The next prime is 21521579. The reversal of 21521568 is 86512512.

It is an interprime number because it is at equal distance from previous prime (21521557) and next prime (21521579).

It is a tau number, because it is divible by the number of its divisors (96).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 259255 + ... + 259337.

It is an arithmetic number, because the mean of its divisors is an integer number (620046).

Almost surely, 2^21521568 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 21521568, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29762208).

21521568 is an abundant number, since it is smaller than the sum of its proper divisors (38002848).

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

21521568 is a wasteful number, since it uses less digits than its factorization.

21521568 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 206 (or 198 counting only the distinct ones).

The product of its digits is 4800, while the sum is 30.

The square root of 21521568 is about 4639.1344020194. The cubic root of 21521568 is about 278.1578387013.

The spelling of 21521568 in words is "twenty-one million, five hundred twenty-one thousand, five hundred sixty-eight".