991235661161 has 2 divisors, whose sum is σ = 991235661162. Its totient is φ = 991235661160.

The previous prime is 991235661029. The next prime is 991235661187. The reversal of 991235661161 is 161166532199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 940087315561 + 51148345600 = 969581^2 + 226160^2 .

It is a cyclic number.

It is not a de Polignac number, because 991235661161 - 2¹⁰ = 991235660137 is a prime.

It is not a weakly prime, because it can be changed into another prime (991235660161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495617830580 + 495617830581.

It is an arithmetic number, because the mean of its divisors is an integer number (495617830581).

Almost surely, 2^991235661161 is an apocalyptic number.

It is an amenable number.

991235661161 is a deficient number, since it is larger than the sum of its proper divisors (1).

991235661161 is an equidigital number, since it uses as much as digits as its factorization.

991235661161 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 524880, while the sum is 50.

The spelling of 991235661161 in words is "nine hundred ninety-one billion, two hundred thirty-five million, six hundred sixty-one thousand, one hundred sixty-one".