21845 is nontrivially palindromic in base 2, base 4, base 8 and base 16.
21845 is an esthetic number in base 2, because in such base its adjacent digits differ by 1.
It is a sphenic number, since it is the product of 3 distinct primes.
It is a 7-Lehmer number, since φ(21845) divides (21845-1)7.
It is a cyclic number.
It is the 16-th Jacobsthal number.
It is a Duffinian number.
21845 is an undulating number in base 2 and base 8.
It is a Curzon number.
21845 is a nontrivial repdigit in base 4 and base 16.
It is a plaindrome in base 4 and base 16.
It is a nialpdrome in base 4 and base 16.
It is a zygodrome in base 4 and base 16.
It is a congruent number.
In principle, a polygon with 21845 sides can be constructed with ruler and compass.
21845 is a Friedman number, since it can be written as (4^8-1)/(5-2), using all its digits and the basic arithmetic operations.
221845 is an apocalyptic number.
It is an amenable number.
21845 is a wasteful number, since it uses less digits than its factorization.
21845 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 279.
The square root of 21845 is about 147.8005412710. The cubic root of 21845 is about 27.9544326865.
The spelling of 21845 in words is "twenty-one thousand, eight hundred forty-five".