8001991 has 2 divisors, whose sum is σ = 8001992. Its totient is φ = 8001990.

The previous prime is 8001971. The next prime is 8002003. The reversal of 8001991 is 1991008.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 8001991 - 2⁷ = 8001863 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (8001911) 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 as a sum of consecutive naturals, namely, 4000995 + 4000996.

It is an arithmetic number, because the mean of its divisors is an integer number (4000996).

Almost surely, 2^8001991 is an apocalyptic number.

8001991 is a deficient number, since it is larger than the sum of its proper divisors (1).

8001991 is an equidigital number, since it uses as much as digits as its factorization.

8001991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 28.

The square root of 8001991 is about 2828.7790652506. The cubic root of 8001991 is about 200.0165902904.

Adding to 8001991 its reverse (1991008), we get a palindrome (9992999).

The spelling of 8001991 in words is "eight million, one thousand, nine hundred ninety-one".