991288129921 has 2 divisors, whose sum is σ = 991288129922. Its totient is φ = 991288129920.

The previous prime is 991288129817. The next prime is 991288130009. The reversal of 991288129921 is 129921882199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 720862129296 + 270426000625 = 849036^2 + 520025^2 .

It is an emirp because it is prime and its reverse (129921882199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991288129921 - 2²⁵ = 991254575489 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991288129921.

It is not a weakly prime, because it can be changed into another prime (991288129621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495644064960 + 495644064961.

It is an arithmetic number, because the mean of its divisors is an integer number (495644064961).

Almost surely, 2^991288129921 is an apocalyptic number.

It is an amenable number.

991288129921 is a deficient number, since it is larger than the sum of its proper divisors (1).

991288129921 is an equidigital number, since it uses as much as digits as its factorization.

991288129921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3359232, while the sum is 61.

The spelling of 991288129921 in words is "nine hundred ninety-one billion, two hundred eighty-eight million, one hundred twenty-nine thousand, nine hundred twenty-one".