3921 has 4 divisors (see below), whose sum is σ = 5232. Its totient is φ = 2612.

The previous prime is 3919. The next prime is 3923. The reversal of 3921 is 1293.

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: 1293 = 3 ⋅431.

It is an interprime number because it is at equal distance from previous prime (3919) and next prime (3923).

It is a cyclic number.

It is not a de Polignac number, because 3921 - 2¹ = 3919 is a prime.

It is a D-number.

It is a plaindrome in base 15.

It is a nialpdrome in base 8 and base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 3921.

It is not an unprimeable number, because it can be changed into a prime (3923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 651 + ... + 656.

It is an arithmetic number, because the mean of its divisors is an integer number (1308).

2³⁹²¹ is an apocalyptic number.

It is an amenable number.

3921 is a deficient number, since it is larger than the sum of its proper divisors (1311).

3921 is a wasteful number, since it uses less digits than its factorization.

3921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1310.

The product of its digits is 54, while the sum is 15.

The square root of 3921 is about 62.6178888178. The cubic root of 3921 is about 15.7688109835.

Subtracting from 3921 its reverse (1293), we obtain a triangular number (2628 = T₇₂).

It can be divided in two parts, 392 and 1, that added together give a palindrome (393).

The spelling of 3921 in words is "three thousand, nine hundred twenty-one".