3891 has 4 divisors (see below), whose sum is σ = 5192.
Its totient is φ = 2592.
The previous prime is 3889. The next prime is 3907. The reversal of 3891 is 1983.
Multipling 3891 by its product of digits (216), we get a triangular number (840456 = T1296).
3891 is nontrivially palindromic in base 6.
It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1983 = 3 ⋅661.
It is not a de Polignac number, because 3891 - 21 = 3889 is a prime.
It is a D-number.
It is a Duffinian number.
3891 is a lucky number.
It is a plaindrome in base 14 and base 15.
It is a nialpdrome in base 16.
It is a zygodrome in base 2.
It is not an unprimeable number, because it can be changed into a prime (3821) 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, 646 + ... + 651.
It is an arithmetic number, because the mean of its divisors is an integer number (1298).
23891 is an apocalyptic number.
3891 is a deficient number, since it is larger than the sum of its proper divisors (1301).
3891 is a wasteful number, since it uses less digits than its factorization.
3891 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1300.
The product of its digits is 216, while the sum is 21.
The square root of 3891 is about 62.3778806950.
The cubic root of 3891 is about 15.7284916795.
The spelling of 3891 in words is "three thousand, eight hundred ninety-one".