21079845721 has 27 divisors (see below), whose sum is σ = 23641401567. Its totient is φ = 18781649040.

The previous prime is 21079845673. The next prime is 21079845733. The reversal of 21079845721 is 12754897012.

The square root of 21079845721 is 145189.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 20654001225 + 425844496 = 143715^2 + 20636^2 .

It is not a de Polignac number, because 21079845721 - 2⁷ = 21079845593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21079840721) by changing a digit.

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 26 ways as a sum of consecutive naturals, for example, 107004195 + ... + 107004391.

Almost surely, 2^21079845721 is an apocalyptic number.

21079845721 is the 145189-th square number.

21079845721 is the 72595-th centered octagonal number.

It is an amenable number.

21079845721 is a deficient number, since it is larger than the sum of its proper divisors (2561555846).

21079845721 is an frugal number, since it uses more digits than its factorization.

21079845721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 550 (or 275 counting only the distinct ones).

The product of its (nonzero) digits is 282240, while the sum is 46.

The spelling of 21079845721 in words is "twenty-one billion, seventy-nine million, eight hundred forty-five thousand, seven hundred twenty-one".