3981 has 4 divisors (see below), whose sum is σ = 5312. Its totient is φ = 2652.

The previous prime is 3967. The next prime is 3989. The reversal of 3981 is 1893.

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: 1893 = 3 ⋅631.

It is not a de Polignac number, because 3981 - 2⁶ = 3917 is a prime.

It is a super-2 number, since 2×3981² = 31696722, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a Curzon number.

3981 is a lucky number.

It is a plaindrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3989) 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, 661 + ... + 666.

It is an arithmetic number, because the mean of its divisors is an integer number (1328).

2³⁹⁸¹ is an apocalyptic number.

It is an amenable number.

3981 is a deficient number, since it is larger than the sum of its proper divisors (1331).

3981 is a wasteful number, since it uses less digits than its factorization.

3981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1330.

The product of its digits is 216, while the sum is 21.

The square root of 3981 is about 63.0951662174. The cubic root of 3981 is about 15.8488367691.

It can be divided in two parts, 39 and 81, that added together give a triangular number (120 = T₁₅).

The spelling of 3981 in words is "three thousand, nine hundred eighty-one".