2021205715721 has 4 divisors (see below), whose sum is σ = 2022839674692. Its totient is φ = 2019571756752.

The previous prime is 2021205715691. The next prime is 2021205715747. The reversal of 2021205715721 is 1275175021202.

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 1364399205625 + 656806510096 = 1168075^2 + 810436^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2021205715721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2021205715421) 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 3 ways as a sum of consecutive naturals, for example, 816977630 + ... + 816980103.

It is an arithmetic number, because the mean of its divisors is an integer number (505709918673).

Almost surely, 2^{2021205715721} is an apocalyptic number.

It is an amenable number.

2021205715721 is a deficient number, since it is larger than the sum of its proper divisors (1633958971).

2021205715721 is a wasteful number, since it uses less digits than its factorization.

2021205715721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1633958970.

The product of its (nonzero) digits is 19600, while the sum is 35.

The spelling of 2021205715721 in words is "two trillion, twenty-one billion, two hundred five million, seven hundred fifteen thousand, seven hundred twenty-one".