21564 has 18 divisors (see below), whose sum is σ = 54600. Its totient is φ = 7176.
The previous prime is 21563. The next prime is 21569. The reversal of 21564 is 46512.
It is a happy number.
It is a tau number, because it is divible by the number of its divisors (18).
It is a Harshad number since it is a multiple of its sum of digits (18).
It is a d-powerful number, because it can be written as 211 + 1 + 55 + 6 + 47 .
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 pernicious number, because its binary representation contains a prime number (7) of ones.
It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 264 + ... + 335.
221564 is an apocalyptic number.
It is an amenable number.
21564 is an abundant number, since it is smaller than the sum of its proper divisors (33036).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
21564 is a wasteful number, since it uses less digits than its factorization.
21564 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 609 (or 604 counting only the distinct ones).
The product of its digits is 240, while the sum is 18.
The square root of 21564 is about 146.8468590062. The cubic root of 21564 is about 27.8340524354.
It can be divided in two parts, 21 and 564, that added together give a palindrome (585).
The spelling of 21564 in words is "twenty-one thousand, five hundred sixty-four".
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