3991781 has 4 divisors (see below), whose sum is σ = 3996864. Its totient is φ = 3986700.

The previous prime is 3991751. The next prime is 3991807. The reversal of 3991781 is 1871993.

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 a cyclic number.

It is not a de Polignac number, because 3991781 - 2⁶ = 3991717 is a prime.

It is a super-2 number, since 2×3991781² = 31868631103922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3991711) 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 in 3 ways as a sum of consecutive naturals, for example, 1085 + ... + 3026.

It is an arithmetic number, because the mean of its divisors is an integer number (999216).

Almost surely, 2^3991781 is an apocalyptic number.

It is an amenable number.

3991781 is a deficient number, since it is larger than the sum of its proper divisors (5083).

3991781 is an equidigital number, since it uses as much as digits as its factorization.

3991781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5082.

The product of its digits is 13608, while the sum is 38.

The square root of 3991781 is about 1997.9441934148. The cubic root of 3991781 is about 158.6313069013.

The spelling of 3991781 in words is "three million, nine hundred ninety-one thousand, seven hundred eighty-one".