91978991 has 8 divisors (see below), whose sum is σ = 99129744. Its totient is φ = 84839040.

The previous prime is 91978987. The next prime is 91979029. The reversal of 91978991 is 19987919.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 91978991 - 2² = 91978987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91978961) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27911 + ... + 31031.

It is an arithmetic number, because the mean of its divisors is an integer number (12391218).

Almost surely, 2^91978991 is an apocalyptic number.

91978991 is a deficient number, since it is larger than the sum of its proper divisors (7150753).

91978991 is a wasteful number, since it uses less digits than its factorization.

91978991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5401.

The product of its digits is 367416, while the sum is 53.

The square root of 91978991 is about 9590.5678142642. The cubic root of 91978991 is about 451.4013778388.

The spelling of 91978991 in words is "ninety-one million, nine hundred seventy-eight thousand, nine hundred ninety-one".