991000009771 has 2 divisors, whose sum is σ = 991000009772. Its totient is φ = 991000009770.

The previous prime is 991000009733. The next prime is 991000009787. The reversal of 991000009771 is 177900000199.

991000009771 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 991000009771 - 2¹⁷ = 990999878699 is a prime.

It is a super-2 number, since 2×991000009771² (a number of 25 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (991000009711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495500004885 + 495500004886.

It is an arithmetic number, because the mean of its divisors is an integer number (495500004886).

Almost surely, 2^991000009771 is an apocalyptic number.

991000009771 is a deficient number, since it is larger than the sum of its proper divisors (1).

991000009771 is an equidigital number, since it uses as much as digits as its factorization.

991000009771 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 35721, while the sum is 43.

The spelling of 991000009771 in words is "nine hundred ninety-one billion, nine thousand, seven hundred seventy-one".