921 has 4 divisors (see below), whose sum is σ = 1232. Its totient is φ = 612.

The previous prime is 919. The next prime is 929. The reversal of 921 is 129.

It is a happy number.

921 is an esthetic number in base 4, 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: 129 = 3 ⋅43.

It is not a de Polignac number, because 921 - 2¹ = 919 is a prime.

It is a D-number.

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

It is a Duffinian number.

It is a plaindrome in base 9, base 13, base 14 and base 16.

It is a nialpdrome in base 10.

It is a junction number, because it is equal to n+sod(n) for n = 897 and 906.

It is not an unprimeable number, because it can be changed into a prime (929) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 151 + ... + 156.

It is an arithmetic number, because the mean of its divisors is an integer number (308).

It is an amenable number.

921 is a deficient number, since it is larger than the sum of its proper divisors (311).

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

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

The sum of its prime factors is 310.

The product of its digits is 18, while the sum is 12.

The square root of 921 is about 30.3479818110. The cubic root of 921 is about 9.7294108588.

Subtracting from 921 its sum of digits (12), we obtain a palindrome (909).

Adding to 921 its product of digits (18), we get a palindrome (939).

Subtracting from 921 its product of digits (18), we obtain a triangular number (903 = T₄₂).

The spelling of 921 in words is "nine hundred twenty-one", and thus it is an aban number.