91000000991 has 2 divisors, whose sum is σ = 91000000992. Its totient is φ = 91000000990.

The previous prime is 91000000981. The next prime is 91000001017. The reversal of 91000000991 is 19900000019.

It is a weak prime.

It is an emirp because it is prime and its reverse (19900000019) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91000000991 - 2³⁴ = 73820131807 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91000000921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45500000495 + 45500000496.

It is an arithmetic number, because the mean of its divisors is an integer number (45500000496).

Almost surely, 2^91000000991 is an apocalyptic number.

91000000991 is a deficient number, since it is larger than the sum of its proper divisors (1).

91000000991 is an equidigital number, since it uses as much as digits as its factorization.

91000000991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 729, while the sum is 29.

The spelling of 91000000991 in words is "ninety-one billion, nine hundred ninety-one", and thus it is an aban number.