21023 has 2 divisors, whose sum is σ = 21024. Its totient is φ = 21022.

The previous prime is 21019. The next prime is 21031. The reversal of 21023 is 32012.

It is an a-pointer prime, because the next prime (21031) can be obtained adding 21023 to its sum of digits (8).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21023 - 2² = 21019 is a prime.

It is a nialpdrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 21023.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21013) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10511 + 10512.

It is an arithmetic number, because the mean of its divisors is an integer number (10512).

2²¹⁰²³ is an apocalyptic number.

21023 is a deficient number, since it is larger than the sum of its proper divisors (1).

21023 is an equidigital number, since it uses as much as digits as its factorization.

21023 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12, while the sum is 8.

The square root of 21023 is about 144.9931032843. The cubic root of 21023 is about 27.5993103517.

Adding to 21023 its reverse (32012), we get a palindrome (53035).

The spelling of 21023 in words is "twenty-one thousand, twenty-three", and thus it is an iban number.