21089 has 2 divisors, whose sum is σ = 21090. Its totient is φ = 21088.

The previous prime is 21067. The next prime is 21101. The reversal of 21089 is 98012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21025 + 64 = 145^2 + 8^2 .

It is a cyclic number.

It is not a de Polignac number, because 21089 - 2¹² = 16993 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21089.

It is not a weakly prime, because it can be changed into another prime (21019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10544 + 10545.

It is an arithmetic number, because the mean of its divisors is an integer number (10545).

2²¹⁰⁸⁹ is an apocalyptic number.

It is an amenable number.

21089 is a deficient number, since it is larger than the sum of its proper divisors (1).

21089 is an equidigital number, since it uses as much as digits as its factorization.

21089 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 21089 is about 145.2205219657. The cubic root of 21089 is about 27.6281621108.

The spelling of 21089 in words is "twenty-one thousand, eighty-nine".