21564221 has 16 divisors (see below), whose sum is σ = 26079360. Its totient is φ = 17418240.

The previous prime is 21564217. The next prime is 21564227. The reversal of 21564221 is 12246512.

It is a happy number.

It is not a de Polignac number, because 21564221 - 2² = 21564217 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21564227) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37085 + ... + 37661.

It is an arithmetic number, because the mean of its divisors is an integer number (1629960).

Almost surely, 2^21564221 is an apocalyptic number.

It is an amenable number.

21564221 is a deficient number, since it is larger than the sum of its proper divisors (4515139).

21564221 is a wasteful number, since it uses less digits than its factorization.

21564221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 884.

The product of its digits is 960, while the sum is 23.

The square root of 21564221 is about 4643.7292126049. The cubic root of 21564221 is about 278.3414752141.

The spelling of 21564221 in words is "twenty-one million, five hundred sixty-four thousand, two hundred twenty-one".