21699 has 6 divisors (see below), whose sum is σ = 31356. Its totient is φ = 14460.

The previous prime is 21683. The next prime is 21701. The reversal of 21699 is 99612.

It is a happy number.

It is not a de Polignac number, because 21699 - 2⁴ = 21683 is a prime.

It is a plaindrome in base 15.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21699.

It is not an unprimeable number, because it can be changed into a prime (21649) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1197 + ... + 1214.

It is an arithmetic number, because the mean of its divisors is an integer number (5226).

2²¹⁶⁹⁹ is an apocalyptic number.

21699 is a deficient number, since it is larger than the sum of its proper divisors (9657).

21699 is a wasteful number, since it uses less digits than its factorization.

21699 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2417 (or 2414 counting only the distinct ones).

The product of its digits is 972, while the sum is 27.

The square root of 21699 is about 147.3058043663. The cubic root of 21699 is about 27.8920160606.

The spelling of 21699 in words is "twenty-one thousand, six hundred ninety-nine".