2121720066721 has 4 divisors (see below), whose sum is σ = 2166863046912. Its totient is φ = 2076577086532.

The previous prime is 2121720066701. The next prime is 2121720066727. The reversal of 2121720066721 is 1276600271212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2121720066721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2121720066727) 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, 22571490025 + ... + 22571490118.

It is an arithmetic number, because the mean of its divisors is an integer number (541715761728).

Almost surely, 2^{2121720066721} is an apocalyptic number.

It is an amenable number.

2121720066721 is a deficient number, since it is larger than the sum of its proper divisors (45142980191).

2121720066721 is an equidigital number, since it uses as much as digits as its factorization.

2121720066721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45142980190.

The product of its (nonzero) digits is 28224, while the sum is 37.

The spelling of 2121720066721 in words is "two trillion, one hundred twenty-one billion, seven hundred twenty million, sixty-six thousand, seven hundred twenty-one".