3991991 has 12 divisors (see below), whose sum is σ = 4361472. Its totient is φ = 3640896.

The previous prime is 3991973. The next prime is 3991993. The reversal of 3991991 is 1991993.

It is not a de Polignac number, because 3991991 - 2¹⁰ = 3990967 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3991993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 31370 + ... + 31496.

It is an arithmetic number, because the mean of its divisors is an integer number (363456).

Almost surely, 2^3991991 is an apocalyptic number.

3991991 is a deficient number, since it is larger than the sum of its proper divisors (369481).

3991991 is a wasteful number, since it uses less digits than its factorization.

3991991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 230 (or 187 counting only the distinct ones).

The product of its digits is 19683, while the sum is 41.

The square root of 3991991 is about 1997.9967467441. The cubic root of 3991991 is about 158.6340886162.

The spelling of 3991991 in words is "three million, nine hundred ninety-one thousand, nine hundred ninety-one".