21559 has 2 divisors, whose sum is σ = 21560. Its totient is φ = 21558.

The previous prime is 21557. The next prime is 21563. The reversal of 21559 is 95512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21559 - 2¹ = 21557 is a prime.

Together with 21557, it forms a pair of twin primes.

It is a Chen prime.

It is a plaindrome in base 14.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10779 + 10780.

It is an arithmetic number, because the mean of its divisors is an integer number (10780).

2²¹⁵⁵⁹ is an apocalyptic number.

21559 is a deficient number, since it is larger than the sum of its proper divisors (1).

21559 is an equidigital number, since it uses as much as digits as its factorization.

21559 is an evil number, because the sum of its binary digits is even.

The product of its digits is 450, while the sum is 22.

The square root of 21559 is about 146.8298334808. The cubic root of 21559 is about 27.8319009944.

The spelling of 21559 in words is "twenty-one thousand, five hundred fifty-nine".