991821106811 has 2 divisors, whose sum is σ = 991821106812. Its totient is φ = 991821106810.

The previous prime is 991821106789. The next prime is 991821106819. The reversal of 991821106811 is 118601128199.

It is a strong prime.

It is an emirp because it is prime and its reverse (118601128199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991821106811 - 2¹⁴ = 991821090427 is a prime.

It is not a weakly prime, because it can be changed into another prime (991821106819) 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, 495910553405 + 495910553406.

It is an arithmetic number, because the mean of its divisors is an integer number (495910553406).

Almost surely, 2^991821106811 is an apocalyptic number.

991821106811 is a deficient number, since it is larger than the sum of its proper divisors (1).

991821106811 is an equidigital number, since it uses as much as digits as its factorization.

991821106811 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 62208, while the sum is 47.

The spelling of 991821106811 in words is "nine hundred ninety-one billion, eight hundred twenty-one million, one hundred six thousand, eight hundred eleven".