3947991 has 8 divisors (see below), whose sum is σ = 5541120. Its totient is φ = 2493432.

The previous prime is 3947987. The next prime is 3948071. The reversal of 3947991 is 1997493.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 3947991 - 2² = 3947987 is a prime.

3947991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3947921) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 34575 + ... + 34688.

It is an arithmetic number, because the mean of its divisors is an integer number (692640).

Almost surely, 2^3947991 is an apocalyptic number.

3947991 is a deficient number, since it is larger than the sum of its proper divisors (1593129).

3947991 is a wasteful number, since it uses less digits than its factorization.

3947991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69285.

The product of its digits is 61236, while the sum is 42.

The square root of 3947991 is about 1986.9552083527. The cubic root of 3947991 is about 158.0491088067.

It can be divided in two parts, 394 and 7991, that added together give a triangular number (8385 = T₁₂₉).

The spelling of 3947991 in words is "three million, nine hundred forty-seven thousand, nine hundred ninety-one".