21564617 has 4 divisors (see below), whose sum is σ = 21868416. Its totient is φ = 21260820.

The previous prime is 21564607. The next prime is 21564637. The reversal of 21564617 is 71646512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21564617 - 2¹⁶ = 21499081 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21564607) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 151793 + ... + 151934.

It is an arithmetic number, because the mean of its divisors is an integer number (5467104).

Almost surely, 2^21564617 is an apocalyptic number.

It is an amenable number.

21564617 is a deficient number, since it is larger than the sum of its proper divisors (303799).

21564617 is an equidigital number, since it uses as much as digits as its factorization.

21564617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 303798.

The product of its digits is 10080, while the sum is 32.

The square root of 21564617 is about 4643.7718505542. The cubic root of 21564617 is about 278.3431790016.

The spelling of 21564617 in words is "twenty-one million, five hundred sixty-four thousand, six hundred seventeen".