7951991 has 4 divisors (see below), whose sum is σ = 8145984. Its totient is φ = 7758000.

The previous prime is 7951973. The next prime is 7952011. The reversal of 7951991 is 1991597.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-7951991 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (41), and also a Moran number because the ratio is a prime number: 193951 = 7951991 / (7 + 9 + 5 + 1 + 9 + 9 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7951901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 96935 + ... + 97016.

It is an arithmetic number, because the mean of its divisors is an integer number (2036496).

Almost surely, 2^7951991 is an apocalyptic number.

7951991 is a deficient number, since it is larger than the sum of its proper divisors (193993).

7951991 is a wasteful number, since it uses less digits than its factorization.

7951991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 193992.

The product of its digits is 25515, while the sum is 41.

The square root of 7951991 is about 2819.9274813371. The cubic root of 7951991 is about 199.5991220211.

The spelling of 7951991 in words is "seven million, nine hundred fifty-one thousand, nine hundred ninety-one".