321991 has 2 divisors, whose sum is σ = 321992. Its totient is φ = 321990.

The previous prime is 321983. The next prime is 322001. The reversal of 321991 is 199123.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 321991 - 2³ = 321983 is a prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (321901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 160995 + 160996.

It is an arithmetic number, because the mean of its divisors is an integer number (160996).

2³²¹⁹⁹¹ is an apocalyptic number.

321991 is a deficient number, since it is larger than the sum of its proper divisors (1).

321991 is an equidigital number, since it uses as much as digits as its factorization.

321991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 486, while the sum is 25.

The square root of 321991 is about 567.4425081010. The cubic root of 321991 is about 68.5406014294.

The spelling of 321991 in words is "three hundred twenty-one thousand, nine hundred ninety-one".