79991991 has 12 divisors (see below), whose sum is σ = 116321400. Its totient is φ = 52969200.

The previous prime is 79991981. The next prime is 79992001. The reversal of 79991991 is 19919997.

It is an interprime number because it is at equal distance from previous prime (79991981) and next prime (79992001).

It is not a de Polignac number, because 79991991 - 2⁹ = 79991479 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (79991921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 28485 + ... + 31166.

It is an arithmetic number, because the mean of its divisors is an integer number (9693450).

Almost surely, 2^79991991 is an apocalyptic number.

79991991 is a deficient number, since it is larger than the sum of its proper divisors (36329409).

79991991 is a wasteful number, since it uses less digits than its factorization.

79991991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59806 (or 59803 counting only the distinct ones).

The product of its digits is 413343, while the sum is 54.

The square root of 79991991 is about 8943.8241820823. The cubic root of 79991991 is about 430.8725584703.

The spelling of 79991991 in words is "seventy-nine million, nine hundred ninety-one thousand, nine hundred ninety-one".