3991891 has 2 divisors, whose sum is σ = 3991892. Its totient is φ = 3991890.

The previous prime is 3991877. The next prime is 3991943. The reversal of 3991891 is 1981993.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 3991891 - 2¹³ = 3983699 is a prime.

It is an Ulam number.

It is not a weakly prime, because it can be changed into another prime (3991831) 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, 1995945 + 1995946.

It is an arithmetic number, because the mean of its divisors is an integer number (1995946).

Almost surely, 2^3991891 is an apocalyptic number.

3991891 is a deficient number, since it is larger than the sum of its proper divisors (1).

3991891 is an equidigital number, since it uses as much as digits as its factorization.

3991891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 17496, while the sum is 40.

The square root of 3991891 is about 1997.9717215216. The cubic root of 3991891 is about 158.6327640022.

The spelling of 3991891 in words is "three million, nine hundred ninety-one thousand, eight hundred ninety-one".