20721061721 has 12 divisors (see below), whose sum is σ = 21884512692. Its totient is φ = 19615766016.

The previous prime is 20721061687. The next prime is 20721061723. The reversal of 20721061721 is 12716012702.

It can be written as a sum of positive squares in 2 ways, for example, as 3576040000 + 17145021721 = 59800^2 + 130939^2 .

It is a de Polignac number, because none of the positive numbers 2^k-20721061721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20721061723) 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 11 ways as a sum of consecutive naturals, for example, 150596 + ... + 253221.

It is an arithmetic number, because the mean of its divisors is an integer number (1823709391).

Almost surely, 2^20721061721 is an apocalyptic number.

It is an amenable number.

20721061721 is a deficient number, since it is larger than the sum of its proper divisors (1163450971).

20721061721 is an equidigital number, since it uses as much as digits as its factorization.

20721061721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 403960 (or 403937 counting only the distinct ones).

The product of its (nonzero) digits is 2352, while the sum is 29.

The spelling of 20721061721 in words is "twenty billion, seven hundred twenty-one million, sixty-one thousand, seven hundred twenty-one".