3991521 has 8 divisors (see below), whose sum is σ = 5352480. Its totient is φ = 2645792.

The previous prime is 3991517. The next prime is 3991543. The reversal of 3991521 is 1251993.

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

It is a cyclic number.

It is not a de Polignac number, because 3991521 - 2² = 3991517 is a prime.

It is a Curzon number.

3991521 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (3991511) 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, 3180 + ... + 4253.

It is an arithmetic number, because the mean of its divisors is an integer number (669060).

Almost surely, 2^3991521 is an apocalyptic number.

It is an amenable number.

3991521 is a deficient number, since it is larger than the sum of its proper divisors (1360959).

3991521 is a wasteful number, since it uses less digits than its factorization.

3991521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7615.

The product of its digits is 2430, while the sum is 30.

The square root of 3991521 is about 1997.8791254728. The cubic root of 3991521 is about 158.6278627381.

The spelling of 3991521 in words is "three million, nine hundred ninety-one thousand, five hundred twenty-one".