1921 has 4 divisors (see below), whose sum is σ = 2052. Its totient is φ = 1792.

The previous prime is 1913. The next prime is 1931. The reversal of 1921 is 1291.

1921 = 5⁴ + 6⁴.

1921 is nontrivially palindromic in base 6.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 625 + 1296 = 25^2 + 36^2 .

It is a cyclic number.

It is not a de Polignac number, because 1921 - 2³ = 1913 is a prime.

It is a Smith number, since the sum of its digits (13) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

1921 is a lucky number.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (1901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40 + ... + 73.

It is an arithmetic number, because the mean of its divisors is an integer number (513).

It is a Proth number, since it is equal to 15 ⋅ 2⁷ + 1 and 15 < 2⁷.

It is an amenable number.

1921 is a deficient number, since it is larger than the sum of its proper divisors (131).

1921 is a wasteful number, since it uses less digits than its factorization.

1921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130.

The product of its digits is 18, while the sum is 13.

The square root of 1921 is about 43.8292140016. The cubic root of 1921 is about 12.4310874497.

Subtracting from 1921 its reverse (1291), we obtain a triangular number (630 = T₃₅).

The spelling of 1921 in words is "one thousand, nine hundred twenty-one".