21344665561 has 16 divisors (see below), whose sum is σ = 22109274000. Its totient is φ = 20590460928.

The previous prime is 21344665543. The next prime is 21344665577. The reversal of 21344665561 is 16556644312.

It can be written as a sum of positive squares in 8 ways, for example, as 653569225 + 20691096336 = 25565^2 + 143844^2 .

It is not a de Polignac number, because 21344665561 - 2⁹ = 21344665049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21344665541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3265945 + ... + 3272473.

It is an arithmetic number, because the mean of its divisors is an integer number (1381829625).

Almost surely, 2^21344665561 is an apocalyptic number.

It is an amenable number.

21344665561 is a deficient number, since it is larger than the sum of its proper divisors (764608439).

21344665561 is a wasteful number, since it uses less digits than its factorization.

21344665561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7308.

The product of its digits is 518400, while the sum is 43.

The spelling of 21344665561 in words is "twenty-one billion, three hundred forty-four million, six hundred sixty-five thousand, five hundred sixty-one".