21870 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.
It is an Ulam number.
It is an alternating number because its digits alternate between even and odd.
21870 is strictly pandigital in base 6.
It is a plaindrome in base 16.
It is a nialpdrome in base 9.
It is a zygodrome in base 9.
It is a congruent number.
21870 is a Friedman number, since it can be written as 270*81, using all its digits and the basic arithmetic operations.
221870 is an apocalyptic number.
It is a practical number, because each smaller number is the sum of distinct divisors of 21870, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29520).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21870 is an frugal number, since it uses more digits than its factorization.
21870 is an odious number, because the sum of its binary digits is odd.
The square root of 21870 is about 147.8850905264. The cubic root of 21870 is about 27.9650925536.
The spelling of 21870 in words is "twenty-one thousand, eight hundred seventy".