21044560261 has 4 divisors (see below), whose sum is σ = 21166205292. Its totient is φ = 20922915232.

The previous prime is 21044560193. The next prime is 21044560279. The reversal of 21044560261 is 16206544012.

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 20343316900 + 701243361 = 142630^2 + 26481^2 .

It is a cyclic number.

It is not a de Polignac number, because 21044560261 - 2⁷ = 21044560133 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21044560291) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 60822256 + ... + 60822601.

It is an arithmetic number, because the mean of its divisors is an integer number (5291551323).

Almost surely, 2^21044560261 is an apocalyptic number.

It is an amenable number.

21044560261 is a deficient number, since it is larger than the sum of its proper divisors (121645031).

21044560261 is a wasteful number, since it uses less digits than its factorization.

21044560261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 121645030.

The product of its (nonzero) digits is 11520, while the sum is 31.

The spelling of 21044560261 in words is "twenty-one billion, forty-four million, five hundred sixty thousand, two hundred sixty-one".