7981991 has 4 divisors (see below), whose sum is σ = 7990752. Its totient is φ = 7973232.

The previous prime is 7981949. The next prime is 7981999. The reversal of 7981991 is 1991897.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1991897 = 787 ⋅2531.

It is a cyclic number.

It is not a de Polignac number, because 7981991 - 2⁶ = 7981927 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 (7981999) 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, 2831 + ... + 4896.

It is an arithmetic number, because the mean of its divisors is an integer number (1997688).

Almost surely, 2^7981991 is an apocalyptic number.

7981991 is a deficient number, since it is larger than the sum of its proper divisors (8761).

7981991 is a wasteful number, since it uses less digits than its factorization.

7981991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8760.

The product of its digits is 40824, while the sum is 44.

The square root of 7981991 is about 2825.2417595668. The cubic root of 7981991 is about 199.8498122464.

The spelling of 7981991 in words is "seven million, nine hundred eighty-one thousand, nine hundred ninety-one".