3971991 has 4 divisors (see below), whose sum is σ = 5295992. Its totient is φ = 2647992.

The previous prime is 3971983. The next prime is 3971993. The reversal of 3971991 is 1991793.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 3971991 - 2³ = 3971983 is a prime.

It is a D-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 (3971993) 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, 661996 + ... + 662001.

It is an arithmetic number, because the mean of its divisors is an integer number (1323998).

Almost surely, 2^3971991 is an apocalyptic number.

3971991 is a deficient number, since it is larger than the sum of its proper divisors (1324001).

3971991 is a wasteful number, since it uses less digits than its factorization.

3971991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1324000.

The product of its digits is 15309, while the sum is 39.

The square root of 3971991 is about 1992.9854490186. The cubic root of 3971991 is about 158.3687243756.

The spelling of 3971991 in words is "three million, nine hundred seventy-one thousand, nine hundred ninety-one".