91173991 has 2 divisors, whose sum is σ = 91173992. Its totient is φ = 91173990.

The previous prime is 91173983. The next prime is 91173997. The reversal of 91173991 is 19937119.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 91173991 - 2³ = 91173983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91173997) by changing a digit.

It is an upside-down number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45586995 + 45586996.

It is an arithmetic number, because the mean of its divisors is an integer number (45586996).

Almost surely, 2^91173991 is an apocalyptic number.

91173991 is a deficient number, since it is larger than the sum of its proper divisors (1).

91173991 is an equidigital number, since it uses as much as digits as its factorization.

91173991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15309, while the sum is 40.

The square root of 91173991 is about 9548.5072655363. The cubic root of 91173991 is about 450.0806291737.

The spelling of 91173991 in words is "ninety-one million, one hundred seventy-three thousand, nine hundred ninety-one".