3991321 has 2 divisors, whose sum is σ = 3991322. Its totient is φ = 3991320.

The previous prime is 3991313. The next prime is 3991331. The reversal of 3991321 is 1231993.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 3115225 + 876096 = 1765^2 + 936^2 .

It is a cyclic number.

It is not a de Polignac number, because 3991321 - 2³ = 3991313 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 3991321.

It is not a weakly prime, because it can be changed into another prime (3991331) 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 as a sum of consecutive naturals, namely, 1995660 + 1995661.

It is an arithmetic number, because the mean of its divisors is an integer number (1995661).

Almost surely, 2^3991321 is an apocalyptic number.

It is an amenable number.

3991321 is a deficient number, since it is larger than the sum of its proper divisors (1).

3991321 is an equidigital number, since it uses as much as digits as its factorization.

3991321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1458, while the sum is 28.

The square root of 3991321 is about 1997.8290717677. The cubic root of 3991321 is about 158.6252132800.

The spelling of 3991321 in words is "three million, nine hundred ninety-one thousand, three hundred twenty-one".