21399 has 8 divisors (see below), whose sum is σ = 32640. Its totient is φ = 12216.

The previous prime is 21397. The next prime is 21401. The reversal of 21399 is 99312.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21397) and next prime (21401).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21399 - 2¹ = 21397 is a prime.

It is a nialpdrome in base 13.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21399.

It is not an unprimeable number, because it can be changed into a prime (21391) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 489 + ... + 530.

It is an arithmetic number, because the mean of its divisors is an integer number (4080).

2²¹³⁹⁹ is an apocalyptic number.

21399 is a deficient number, since it is larger than the sum of its proper divisors (11241).

21399 is a wasteful number, since it uses less digits than its factorization.

21399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1029.

The product of its digits is 486, while the sum is 24.

The square root of 21399 is about 146.2839704137. The cubic root of 21399 is about 27.7628785284.

The spelling of 21399 in words is "twenty-one thousand, three hundred ninety-nine".