31891 has 2 divisors, whose sum is σ = 31892.
Its totient is φ = 31890.
The previous prime is 31883. The next prime is 31907. The reversal of 31891 is 19813.
It is a weak prime.
It is an emirp because it is prime and its reverse (19813) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 31891 - 23 = 31883 is a prime.
It is a Chen prime.
It is not a weakly prime, because it can be changed into another prime (31091) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15945 + 15946.
It is an arithmetic number, because the mean of its divisors is an integer number (15946).
231891 is an apocalyptic number.
31891 is a deficient number, since it is larger than the sum of its proper divisors (1).
31891 is an equidigital number, since it uses as much as digits as its factorization.
31891 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 216, while the sum is 22.
The square root of 31891 is about 178.5805140546.
The cubic root of 31891 is about 31.7119328009.
Adding to 31891 its sum of digits (22), we get a palindrome (31913).
The spelling of 31891 in words is "thirty-one thousand, eight hundred ninety-one".