21168 divided by its sum of digits (18) gives a triangular number (1176 = T48).
It is a nude number because it is divisible by every one of its digits.
It is a zygodrome in base 7.
It is a self number, because there is not a number n which added to its sum of digits gives 21168.
21168 is an untouchable number, because it is not equal to the sum of proper divisors of any number.
221168 is an apocalyptic number.
21168 is a gapful number since it is divisible by the number (28) formed by its first and last digit.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 21168, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35340).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21168 is a wasteful number, since it uses less digits than its factorization.
21168 is an evil number, because the sum of its binary digits is even.
The square root of 21168 is about 145.4922678358. The cubic root of 21168 is about 27.6626177524.
The spelling of 21168 in words is "twenty-one thousand, one hundred sixty-eight".