7921991 has 24 divisors (see below), whose sum is σ = 10214400. Its totient is φ = 6011280.

The previous prime is 7921987. The next prime is 7921999. The reversal of 7921991 is 1991297.

It is not a de Polignac number, because 7921991 - 2² = 7921987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7921999) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 39710 + ... + 39908.

It is an arithmetic number, because the mean of its divisors is an integer number (425600).

Almost surely, 2^7921991 is an apocalyptic number.

7921991 is a deficient number, since it is larger than the sum of its proper divisors (2292409).

7921991 is a wasteful number, since it uses less digits than its factorization.

7921991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 275 (or 264 counting only the distinct ones).

The product of its digits is 10206, while the sum is 38.

The square root of 7921991 is about 2814.6031691874. The cubic root of 7921991 is about 199.3478004909.

The spelling of 7921991 in words is "seven million, nine hundred twenty-one thousand, nine hundred ninety-one".