21565718641 has 4 divisors (see below), whose sum is σ = 21675189492. Its totient is φ = 21456247792.

The previous prime is 21565718593. The next prime is 21565718651. The reversal of 21565718641 is 14681756512.

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 17470230625 + 4095488016 = 132175^2 + 63996^2 .

It is a cyclic number.

It is not a de Polignac number, because 21565718641 - 2¹¹ = 21565716593 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21565718591 and 21565718600.

It is not an unprimeable number, because it can be changed into a prime (21565718651) 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, 54735130 + ... + 54735523.

It is an arithmetic number, because the mean of its divisors is an integer number (5418797373).

Almost surely, 2^21565718641 is an apocalyptic number.

It is an amenable number.

21565718641 is a deficient number, since it is larger than the sum of its proper divisors (109470851).

21565718641 is a wasteful number, since it uses less digits than its factorization.

21565718641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109470850.

The product of its digits is 403200, while the sum is 46.

The spelling of 21565718641 in words is "twenty-one billion, five hundred sixty-five million, seven hundred eighteen thousand, six hundred forty-one".