21576 has 32 divisors (see below), whose sum is σ = 57600. Its totient is φ = 6720.

The previous prime is 21569. The next prime is 21577. The reversal of 21576 is 67512.

It is a nialpdrome in base 8.

It is a zygodrome in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21577) by changing a digit.

21576 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 681 + ... + 711.

It is an arithmetic number, because the mean of its divisors is an integer number (1800).

2²¹⁵⁷⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21576, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28800).

21576 is an abundant number, since it is smaller than the sum of its proper divisors (36024).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21576 is a wasteful number, since it uses less digits than its factorization.

21576 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69 (or 65 counting only the distinct ones).

The product of its digits is 420, while the sum is 21.

The square root of 21576 is about 146.8877122158. The cubic root of 21576 is about 27.8392145372.

The spelling of 21576 in words is "twenty-one thousand, five hundred seventy-six".