21493 has 2 divisors, whose sum is σ = 21494.
Its totient is φ = 21492.
The previous prime is 21491. The next prime is 21499. The reversal of 21493 is 39412.
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 13924 + 7569 = 118^2 + 87^2
It is a cyclic number.
It is not a de Polignac number, because 21493 - 21 = 21491 is a prime.
Together with 21491, it forms a pair of twin primes.
It is a self number, because there is not a number n which added to its sum of digits gives 21493.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (21491) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10746 + 10747.
It is an arithmetic number, because the mean of its divisors is an integer number (10747).
221493 is an apocalyptic number.
It is an amenable number.
21493 is a deficient number, since it is larger than the sum of its proper divisors (1).
21493 is an equidigital number, since it uses as much as digits as its factorization.
21493 is an evil number, because the sum of its binary digits is even.
The product of its digits is 216, while the sum is 19.
The square root of 21493 is about 146.6049112411.
The cubic root of 21493 is about 27.8034707466.
Adding to 21493 its sum of digits (19), we get a palindrome (21512).
The spelling of 21493 in words is "twenty-one thousand, four hundred ninety-three".