21164380565 has 8 divisors (see below), whose sum is σ = 25402266168. Its totient is φ = 16928164800.

The previous prime is 21164380547. The next prime is 21164380591. The reversal of 21164380565 is 56508346112.

It can be written as a sum of positive squares in 4 ways, for example, as 556629649 + 20607750916 = 23593^2 + 143554^2 .

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

It is not a de Polignac number, because 21164380565 - 2¹⁰ = 21164379541 is a prime.

It is a Duffinian number.

It is a Curzon 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, 389402 + ... + 440411.

It is an arithmetic number, because the mean of its divisors is an integer number (3175283271).

Almost surely, 2^21164380565 is an apocalyptic number.

It is an amenable number.

21164380565 is a deficient number, since it is larger than the sum of its proper divisors (4237885603).

21164380565 is an equidigital number, since it uses as much as digits as its factorization.

21164380565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 834919.

The product of its (nonzero) digits is 172800, while the sum is 41.

The spelling of 21164380565 in words is "twenty-one billion, one hundred sixty-four million, three hundred eighty thousand, five hundred sixty-five".