21567 has 16 divisors (see below), whose sum is σ = 35840. Its totient is φ = 11232.

The previous prime is 21563. The next prime is 21569. The reversal of 21567 is 76512.

21567 is nontrivially palindromic in base 9.

It is not a de Polignac number, because 21567 - 2² = 21563 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

21567 is a modest number, since divided by 567 gives 21 as remainder.

21567 is a lucky number.

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21563) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 234 + ... + 312.

It is an arithmetic number, because the mean of its divisors is an integer number (2240).

2²¹⁵⁶⁷ is an apocalyptic number.

21567 is a deficient number, since it is larger than the sum of its proper divisors (14273).

21567 is a wasteful number, since it uses less digits than its factorization.

21567 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 102.

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

The square root of 21567 is about 146.8570733741. The cubic root of 21567 is about 27.8353431404.

Subtracting 21567 from its reverse (76512), we obtain a palindrome (54945).

It can be divided in two parts, 215 and 67, that added together give a palindrome (282).

The spelling of 21567 in words is "twenty-one thousand, five hundred sixty-seven".