191808528721 has 2 divisors, whose sum is σ = 191808528722. Its totient is φ = 191808528720.

The previous prime is 191808528701. The next prime is 191808528731. The reversal of 191808528721 is 127825808191.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 185123667600 + 6684861121 = 430260^2 + 81761^2 .

It is a cyclic number.

It is not a de Polignac number, because 191808528721 - 2¹⁹ = 191808004433 is a prime.

It is a super-2 number, since 2×191808528721² (a number of 23 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (191808528701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 95904264360 + 95904264361.

It is an arithmetic number, because the mean of its divisors is an integer number (95904264361).

Almost surely, 2^191808528721 is an apocalyptic number.

It is an amenable number.

191808528721 is a deficient number, since it is larger than the sum of its proper divisors (1).

191808528721 is an equidigital number, since it uses as much as digits as its factorization.

191808528721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 645120, while the sum is 52.

The spelling of 191808528721 in words is "one hundred ninety-one billion, eight hundred eight million, five hundred twenty-eight thousand, seven hundred twenty-one".