3991809 has 4 divisors (see below), whose sum is σ = 5322416. Its totient is φ = 2661204.

The previous prime is 3991807. The next prime is 3991817. The reversal of 3991809 is 9081993.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 3991809 - 2¹ = 3991807 is a prime.

It is a D-number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (3991807) 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, 665299 + ... + 665304.

It is an arithmetic number, because the mean of its divisors is an integer number (1330604).

Almost surely, 2^3991809 is an apocalyptic number.

It is an amenable number.

3991809 is a deficient number, since it is larger than the sum of its proper divisors (1330607).

3991809 is a wasteful number, since it uses less digits than its factorization.

3991809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1330606.

The product of its (nonzero) digits is 17496, while the sum is 39.

The square root of 3991809 is about 1997.9512006053. The cubic root of 3991809 is about 158.6316778022.

The spelling of 3991809 in words is "three million, nine hundred ninety-one thousand, eight hundred nine".