21145697665 has 4 divisors (see below), whose sum is σ = 25374837204. Its totient is φ = 16916558128.

The previous prime is 21145697663. The next prime is 21145697689. The reversal of 21145697665 is 56679654112.

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 5689986624 + 15455711041 = 75432^2 + 124321^2 .

It is a cyclic number.

It is not a de Polignac number, because 21145697665 - 2¹ = 21145697663 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21145697663) by changing a digit.

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, 2114569762 + ... + 2114569771.

It is an arithmetic number, because the mean of its divisors is an integer number (6343709301).

Almost surely, 2^21145697665 is an apocalyptic number.

It is an amenable number.

21145697665 is a deficient number, since it is larger than the sum of its proper divisors (4229139539).

21145697665 is an equidigital number, since it uses as much as digits as its factorization.

21145697665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4229139538.

The product of its digits is 2721600, while the sum is 52.

The spelling of 21145697665 in words is "twenty-one billion, one hundred forty-five million, six hundred ninety-seven thousand, six hundred sixty-five".