216721322165681 has 2 divisors, whose sum is σ = 216721322165682. Its totient is φ = 216721322165680.

The previous prime is 216721322165669. The next prime is 216721322165683. The reversal of 216721322165681 is 186561223127612.

216721322165681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 215917045021456 + 804277144225 = 14694116^2 + 896815^2 .

It is a cyclic number.

It is not a de Polignac number, because 216721322165681 - 2⁶ = 216721322165617 is a prime.

It is a super-2 number, since 2×216721322165681² (a number of 29 digits) contains 22 as substring.

Together with 216721322165683, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (216721322165683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108360661082840 + 108360661082841.

It is an arithmetic number, because the mean of its divisors is an integer number (108360661082841).

Almost surely, 2^{216721322165681} is an apocalyptic number.

It is an amenable number.

216721322165681 is a deficient number, since it is larger than the sum of its proper divisors (1).

216721322165681 is an equidigital number, since it uses as much as digits as its factorization.

216721322165681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2903040, while the sum is 53.

The spelling of 216721322165681 in words is "two hundred sixteen trillion, seven hundred twenty-one billion, three hundred twenty-two million, one hundred sixty-five thousand, six hundred eighty-one".