7971991 has 4 divisors (see below), whose sum is σ = 8229184. Its totient is φ = 7714800.

The previous prime is 7971973. The next prime is 7972009. The reversal of 7971991 is 1991797.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (7971973) and next prime (7972009).

It is a cyclic number.

It is not a de Polignac number, because 7971991 - 2⁵ = 7971959 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7971911) 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 3 ways as a sum of consecutive naturals, for example, 128550 + ... + 128611.

It is an arithmetic number, because the mean of its divisors is an integer number (2057296).

Almost surely, 2^7971991 is an apocalyptic number.

7971991 is a deficient number, since it is larger than the sum of its proper divisors (257193).

7971991 is a wasteful number, since it uses less digits than its factorization.

7971991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 257192.

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

The square root of 7971991 is about 2823.4714448707. The cubic root of 7971991 is about 199.7663187383.

The spelling of 7971991 in words is "seven million, nine hundred seventy-one thousand, nine hundred ninety-one".