1391 has 4 divisors (see below), whose sum is σ = 1512. Its totient is φ = 1272.

The previous prime is 1381. The next prime is 1399. The reversal of 1391 is 1931.

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

It is a cyclic number.

It is not a de Polignac number, because 1391 - 2⁶ = 1327 is a prime.

It is a Duffinian number.

It is a plaindrome in base 4, base 8 and base 16.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1399) 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, 41 + ... + 66.

It is an arithmetic number, because the mean of its divisors is an integer number (378).

1391 is a deficient number, since it is larger than the sum of its proper divisors (121).

1391 is a wasteful number, since it uses less digits than its factorization.

1391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120.

The product of its digits is 27, while the sum is 14.

The square root of 1391 is about 37.2961123979. The cubic root of 1391 is about 11.1628659623.

The spelling of 1391 in words is "one thousand, three hundred ninety-one".