321 has 4 divisors (see below), whose sum is σ = 432. Its totient is φ = 212.

The previous prime is 317. The next prime is 331. The reversal of 321 is 123.

321 is nontrivially palindromic in base 7, base 11 and base 16.

321 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 123 = 3 ⋅41.

It is a cyclic number.

It is not a de Polignac number, because 321 - 2² = 317 is a prime.

It is a D-number.

It is an alternating number because its digits alternate between odd and even.

321 is an undulating number in base 7, base 11 and base 16.

It is a Curzon number.

321 is a lucky number.

It is a straight-line number, since its digits are in arithmetic progression.

It is a plaindrome in base 12, base 14 and base 15.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 51 + ... + 56.

It is an arithmetic number, because the mean of its divisors is an integer number (108).

It is a Proth number, since it is equal to 5 ⋅ 2⁶ + 1 and 5 < 2⁶.

It is an amenable number.

321 is a deficient number, since it is larger than the sum of its proper divisors (111).

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

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

The sum of its prime factors is 110.

The product of its digits is 6, while the sum is 6.

The square root of 321 is about 17.9164728672. The cubic root of 321 is about 6.8470212776.

Adding to 321 its reverse (123), we get a palindrome (444).

It can be divided in two parts, 32 and 1, that added together give a palindrome (33).

The spelling of 321 in words is "three hundred twenty-one", and thus it is an aban number and an iban number.