21565717 has 4 divisors (see below), whose sum is σ = 21579136. Its totient is φ = 21552300.

The previous prime is 21565699. The next prime is 21565721. The reversal of 21565717 is 71756512.

It is a happy number.

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 21565717 - 2¹⁵ = 21532949 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 (21565777) 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, 3909 + ... + 7642.

It is an arithmetic number, because the mean of its divisors is an integer number (5394784).

Almost surely, 2^21565717 is an apocalyptic number.

It is an amenable number.

21565717 is a deficient number, since it is larger than the sum of its proper divisors (13419).

21565717 is a wasteful number, since it uses less digits than its factorization.

21565717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13418.

The product of its digits is 14700, while the sum is 34.

The square root of 21565717 is about 4643.8902872484. The cubic root of 21565717 is about 278.3479116352.

The spelling of 21565717 in words is "twenty-one million, five hundred sixty-five thousand, seven hundred seventeen".