991893805897 has 2 divisors, whose sum is σ = 991893805898. Its totient is φ = 991893805896.

The previous prime is 991893805841. The next prime is 991893805909. The reversal of 991893805897 is 798508398199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 613698325321 + 378195480576 = 783389^2 + 614976^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991893805897 is a prime.

It is not a weakly prime, because it can be changed into another prime (991893805297) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495946902948 + 495946902949.

It is an arithmetic number, because the mean of its divisors is an integer number (495946902949).

Almost surely, 2^991893805897 is an apocalyptic number.

It is an amenable number.

991893805897 is a deficient number, since it is larger than the sum of its proper divisors (1).

991893805897 is an equidigital number, since it uses as much as digits as its factorization.

991893805897 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 352719360, while the sum is 76.

The spelling of 991893805897 in words is "nine hundred ninety-one billion, eight hundred ninety-three million, eight hundred five thousand, eight hundred ninety-seven".