21566 has 8 divisors (see below), whose sum is σ = 33264. Its totient is φ = 10480.

The previous prime is 21563. The next prime is 21569. The reversal of 21566 is 66512.

It is an interprime number because it is at equal distance from previous prime (21563) and next prime (21569).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Curzon number.

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 3 ways as a sum of consecutive naturals, for example, 50 + ... + 213.

It is an arithmetic number, because the mean of its divisors is an integer number (4158).

2²¹⁵⁶⁶ is an apocalyptic number.

21566 is a deficient number, since it is larger than the sum of its proper divisors (11698).

21566 is a wasteful number, since it uses less digits than its factorization.

21566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 306.

The product of its digits is 360, while the sum is 20.

The square root of 21566 is about 146.8536686637. The cubic root of 21566 is about 27.8349129187.

The spelling of 21566 in words is "twenty-one thousand, five hundred sixty-six".