21929 has 2 divisors, whose sum is σ = 21930. Its totient is φ = 21928.

The previous prime is 21911. The next prime is 21937. The reversal of 21929 is 92912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21904 + 25 = 148^2 + 5^2 .

It is a cyclic number.

It is not a de Polignac number, because 21929 - 2⁸ = 21673 is a prime.

It is not a weakly prime, because it can be changed into another prime (21529) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10964 + 10965.

It is an arithmetic number, because the mean of its divisors is an integer number (10965).

2²¹⁹²⁹ is an apocalyptic number.

It is an amenable number.

21929 is a deficient number, since it is larger than the sum of its proper divisors (1).

21929 is an equidigital number, since it uses as much as digits as its factorization.

21929 is an evil number, because the sum of its binary digits is even.

The product of its digits is 324, while the sum is 23.

The square root of 21929 is about 148.0844353739. The cubic root of 21929 is about 27.9902176712.

Adding to 21929 its sum of digits (23), we get a cube (21952 = 28³).

The spelling of 21929 in words is "twenty-one thousand, nine hundred twenty-nine".