Subtracting from 21546 its sum of digits (18), we obtain a triangular number (21528 = T207).
It is a happy number.
It is a Curzon number.
It is a zygodrome in base 4.
It is an unprimeable number.
21546 is an untouchable number, because it is not equal to the sum of proper divisors of any number.
221546 is an apocalyptic number.
It is a practical number, because each smaller number is the sum of distinct divisors of 21546, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29040).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21546 is a wasteful number, since it uses less digits than its factorization.
21546 is an evil number, because the sum of its binary digits is even.
The square root of 21546 is about 146.7855578727. The cubic root of 21546 is about 27.8263056906.
The spelling of 21546 in words is "twenty-one thousand, five hundred forty-six".