21504643565 has 4 divisors (see below), whose sum is σ = 25805572284. Its totient is φ = 17203714848.

The previous prime is 21504643481. The next prime is 21504643577. The reversal of 21504643565 is 56534640512.

It is a happy number.

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 5440095049 + 16064548516 = 73757^2 + 126746^2 .

It is a cyclic number.

It is not a de Polignac number, because 21504643565 - 2⁸ = 21504643309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2150464352 + ... + 2150464361.

It is an arithmetic number, because the mean of its divisors is an integer number (6451393071).

Almost surely, 2^21504643565 is an apocalyptic number.

It is an amenable number.

21504643565 is a deficient number, since it is larger than the sum of its proper divisors (4300928719).

21504643565 is an equidigital number, since it uses as much as digits as its factorization.

21504643565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4300928718.

The product of its (nonzero) digits is 432000, while the sum is 41.

The spelling of 21504643565 in words is "twenty-one billion, five hundred four million, six hundred forty-three thousand, five hundred sixty-five".