21563 has 2 divisors, whose sum is σ = 21564. Its totient is φ = 21562.

The previous prime is 21559. The next prime is 21569. The reversal of 21563 is 36512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21563 - 2² = 21559 is a prime.

It is not a weakly prime, because it can be changed into another prime (21569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10781 + 10782.

It is an arithmetic number, because the mean of its divisors is an integer number (10782).

2²¹⁵⁶³ is an apocalyptic number.

21563 is a deficient number, since it is larger than the sum of its proper divisors (1).

21563 is an equidigital number, since it uses as much as digits as its factorization.

21563 is an evil number, because the sum of its binary digits is even.

The product of its digits is 180, while the sum is 17.

The square root of 21563 is about 146.8434540591. The cubic root of 21563 is about 27.8336221738.

The spelling of 21563 in words is "twenty-one thousand, five hundred sixty-three".