21565718609 has 4 divisors (see below), whose sum is σ = 21690376116. Its totient is φ = 21441061104.

The previous prime is 21565718593. The next prime is 21565718651. The reversal of 21565718609 is 90681756512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15865921600 + 5699797009 = 125960^2 + 75497^2 .

It is a cyclic number.

It is not a de Polignac number, because 21565718609 - 2⁴ = 21565718593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21565718809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 62328494 + ... + 62328839.

It is an arithmetic number, because the mean of its divisors is an integer number (5422594029).

Almost surely, 2^21565718609 is an apocalyptic number.

It is an amenable number.

21565718609 is a deficient number, since it is larger than the sum of its proper divisors (124657507).

21565718609 is a wasteful number, since it uses less digits than its factorization.

21565718609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 124657506.

The product of its (nonzero) digits is 907200, while the sum is 50.

The spelling of 21565718609 in words is "twenty-one billion, five hundred sixty-five million, seven hundred eighteen thousand, six hundred nine".