191591568821 has 2 divisors, whose sum is σ = 191591568822. Its totient is φ = 191591568820.

The previous prime is 191591568787. The next prime is 191591568827. The reversal of 191591568821 is 128865195191.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 150427622500 + 41163946321 = 387850^2 + 202889^2 .

It is an emirp because it is prime and its reverse (128865195191) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-191591568821 is a prime.

It is a super-3 number, since 3×191591568821³ (a number of 35 digits) contains 333 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (191591568827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 95795784410 + 95795784411.

It is an arithmetic number, because the mean of its divisors is an integer number (95795784411).

Almost surely, 2^191591568821 is an apocalyptic number.

It is an amenable number.

191591568821 is a deficient number, since it is larger than the sum of its proper divisors (1).

191591568821 is an equidigital number, since it uses as much as digits as its factorization.

191591568821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1555200, while the sum is 56.

The spelling of 191591568821 in words is "one hundred ninety-one billion, five hundred ninety-one million, five hundred sixty-eight thousand, eight hundred twenty-one".