3987991 has 4 divisors (see below), whose sum is σ = 4557712. Its totient is φ = 3418272.

The previous prime is 3987943. The next prime is 3988003. The reversal of 3987991 is 1997893.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1997893 = 83 ⋅24071.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-3987991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3987931) 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, 284850 + ... + 284863.

It is an arithmetic number, because the mean of its divisors is an integer number (1139428).

Almost surely, 2^3987991 is an apocalyptic number.

3987991 is a deficient number, since it is larger than the sum of its proper divisors (569721).

3987991 is an equidigital number, since it uses as much as digits as its factorization.

3987991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 569720.

The product of its digits is 122472, while the sum is 46.

The square root of 3987991 is about 1996.9954932348. The cubic root of 3987991 is about 158.5810867925.

The spelling of 3987991 in words is "three million, nine hundred eighty-seven thousand, nine hundred ninety-one".