21191 has 2 divisors, whose sum is σ = 21192. Its totient is φ = 21190.

The previous prime is 21187. The next prime is 21193. The reversal of 21191 is 19112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21191 - 2² = 21187 is a prime.

Together with 21193, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21193) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10595 + 10596.

It is an arithmetic number, because the mean of its divisors is an integer number (10596).

2²¹¹⁹¹ is an apocalyptic number.

21191 is a deficient number, since it is larger than the sum of its proper divisors (1).

21191 is an equidigital number, since it uses as much as digits as its factorization.

21191 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18, while the sum is 14.

The square root of 21191 is about 145.5712883779. The cubic root of 21191 is about 27.6726330256.

It can be divided in two parts, 21 and 191, that added together give a palindrome (212).

The spelling of 21191 in words is "twenty-one thousand, one hundred ninety-one".