21765120565 has 8 divisors (see below), whose sum is σ = 26126531928. Its totient is φ = 17406504960.

The previous prime is 21765120497. The next prime is 21765120581. The reversal of 21765120565 is 56502156712.

It can be written as a sum of positive squares in 4 ways, for example, as 1284362244 + 20480758321 = 35838^2 + 143111^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21765120565 - 2⁹ = 21765120053 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 681772 + ... + 712981.

It is an arithmetic number, because the mean of its divisors is an integer number (3265816491).

Almost surely, 2^21765120565 is an apocalyptic number.

It is an amenable number.

21765120565 is a deficient number, since it is larger than the sum of its proper divisors (4361411363).

21765120565 is a wasteful number, since it uses less digits than its factorization.

21765120565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1397879.

The product of its (nonzero) digits is 126000, while the sum is 40.

The spelling of 21765120565 in words is "twenty-one billion, seven hundred sixty-five million, one hundred twenty thousand, five hundred sixty-five".