21599 has 2 divisors, whose sum is σ = 21600. Its totient is φ = 21598.

The previous prime is 21589. The next prime is 21601. The reversal of 21599 is 99512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21599 is a prime.

Together with 21601, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

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, 10799 + 10800.

It is an arithmetic number, because the mean of its divisors is an integer number (10800).

2²¹⁵⁹⁹ is an apocalyptic number.

21599 is a deficient number, since it is larger than the sum of its proper divisors (1).

21599 is an equidigital number, since it uses as much as digits as its factorization.

21599 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 810, while the sum is 26.

The square root of 21599 is about 146.9659824585. The cubic root of 21599 is about 27.8491032183.

The spelling of 21599 in words is "twenty-one thousand, five hundred ninety-nine".