19891 has 2 divisors, whose sum is σ = 19892. Its totient is φ = 19890.

The previous prime is 19889. The next prime is 19913.

19891 is nontrivially palindromic in base 10.

It is a weak prime.

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 19891 - 2¹ = 19889 is a prime.

Together with 19889, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (19801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9945 + 9946.

It is an arithmetic number, because the mean of its divisors is an integer number (9946).

2¹⁹⁸⁹¹ is an apocalyptic number.

19891 is a deficient number, since it is larger than the sum of its proper divisors (1).

19891 is an equidigital number, since it uses as much as digits as its factorization.

19891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 648, while the sum is 28.

The square root of 19891 is about 141.0354565349. The cubic root of 19891 is about 27.0947743904.

It can be divided in two parts, 198 and 91, that added together give a square (289 = 17²).

The spelling of 19891 in words is "nineteen thousand, eight hundred ninety-one".