7991891 has 2 divisors, whose sum is σ = 7991892. Its totient is φ = 7991890.

The previous prime is 7991869. The next prime is 7991897. The reversal of 7991891 is 1981997.

It is a strong prime.

It is an emirp because it is prime and its reverse (1981997) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 7991891 - 2¹⁴ = 7975507 is a prime.

It is a super-3 number, since 3×7991891³ (a number of 22 digits) contains 333 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (7991897) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3995945 + 3995946.

It is an arithmetic number, because the mean of its divisors is an integer number (3995946).

Almost surely, 2^7991891 is an apocalyptic number.

7991891 is a deficient number, since it is larger than the sum of its proper divisors (1).

7991891 is an equidigital number, since it uses as much as digits as its factorization.

7991891 is an evil number, because the sum of its binary digits is even.

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

The square root of 7991891 is about 2826.9932790865. The cubic root of 7991891 is about 199.9324021552.

The spelling of 7991891 in words is "seven million, nine hundred ninety-one thousand, eight hundred ninety-one".