7917991 has 4 divisors (see below), whose sum is σ = 8029584. Its totient is φ = 7806400.

The previous prime is 7917967. The next prime is 7917997. The reversal of 7917991 is 1997197.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1997197 = 157 ⋅12721.

It is a cyclic number.

It is not a de Polignac number, because 7917991 - 2⁷ = 7917863 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 (7917997) 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, 55690 + ... + 55831.

It is an arithmetic number, because the mean of its divisors is an integer number (2007396).

Almost surely, 2^7917991 is an apocalyptic number.

7917991 is a gapful number since it is divisible by the number (71) formed by its first and last digit.

7917991 is a deficient number, since it is larger than the sum of its proper divisors (111593).

7917991 is a wasteful number, since it uses less digits than its factorization.

7917991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 111592.

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

The square root of 7917991 is about 2813.8924997235. The cubic root of 7917991 is about 199.3142430410.

The spelling of 7917991 in words is "seven million, nine hundred seventeen thousand, nine hundred ninety-one".