21103947665 has 4 divisors (see below), whose sum is σ = 25324737204. Its totient is φ = 16883158128.

The previous prime is 21103947649. The next prime is 21103947673. The reversal of 21103947665 is 56674930112.

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 10382794816 + 10721152849 = 101896^2 + 103543^2 .

It is a cyclic number.

It is not a de Polignac number, because 21103947665 - 2⁴ = 21103947649 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2110394762 + ... + 2110394771.

It is an arithmetic number, because the mean of its divisors is an integer number (6331184301).

Almost surely, 2^21103947665 is an apocalyptic number.

It is an amenable number.

21103947665 is a deficient number, since it is larger than the sum of its proper divisors (4220789539).

21103947665 is an equidigital number, since it uses as much as digits as its factorization.

21103947665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4220789538.

The product of its (nonzero) digits is 272160, while the sum is 44.

The spelling of 21103947665 in words is "twenty-one billion, one hundred three million, nine hundred forty-seven thousand, six hundred sixty-five".